Linux Virtualization - Jan 2016 - [PATCH v3 00/41] arch: barrier cleanup + barriers for virt

Changes since v2:
	- extended checkpatch tests for barriers, and added patches
	teaching it to warn about incorrect usage of barriers
	(__smp_xxx barriers are for use by asm-generic code only),
	should help prevent misuse by arch code
	to address comments by Russell King
	- patched more instances of xen to use virt_ barriers
	as suggested by  Stefano Stabellini
	- implemented a 2 byte xchg on sh instead of hacking around it
	as suggested by Peter Zijlstra and  Rich Felker
	- added a patch to drop some s390 arch-specific smp_xxx barriers - generic
	versions are more efficient
	as suggested by Peter Zijlstra and Martin Schwidefsky
	- added a patch to replace before/after atomic barriers with barrier()
	on s390 as suggested by Peter Zijlstra and Martin Schwidefsky
	- included acks from multiple arch maintainers
	thanks a lot for the review!

Changes since v1:
	- replaced an asm-generic patch with an equivalent patch already in tip
	- add wrappers with virt_ prefix for better code annotation,
	  as suggested by David Miller
	- dropped XXX in patch names as this makes vger choke, Cc all relevant
	  mailing lists on all patches (not personal email, as the list becomes
	  too long then)

I parked this in vhost tree for now, though the inclusion of patch 1 from tip
creates a merge conflict - but one that is trivial to resolve.

So I intend to just merge it all through my tree, including the
duplicate patch, and assume conflict will be resolved.

I would really appreciate some feedback on arch bits (especially the x86 bits),
and acks for merging this through the vhost tree.

Thanks!

What really started me off is trying to cleanup some virt code, as suggested by
Peter, who said
> You could of course go fix that instead of mutilating things into
> sort-of functional state.
This work is needed for virtio, so it's probably easiest to
merge it through my tree - is this fine by everyone?

Note to arch maintainers: please don't cherry-pick patches out of this
patchset
as it's been structured in this order to avoid breaking bisect.
Please send acks instead!

====
Sometimes, virtualization is weird. For example, virtio does this
(conceptually):

#ifdef CONFIG_SMP
                smp_mb();
#else
                mb();
#endif

Similarly, Xen calls mb() when it's not doing any MMIO at all.

Of course it's wrong in the sense that it's suboptimal. What we would
really
like is to have, on UP, exactly the same barrier as on SMP.  This is because a
UP guest can run on an SMP host.

But Linux doesn't provide this ability: if CONFIG_SMP is not defined is
optimizes most barriers out to a compiler barrier.

Consider for example x86: what we want is xchg (NOT mfence - there's no real
IO
going on here - just switching out of the VM - more like a function call
really) but if built without CONFIG_SMP smp_store_mb does not include this.

Virt in general is probably the only use-case, because this really is an
artifact of interfacing with an SMP host while running an UP kernel,
but since we have (at least) two users, it seems to make sense to
put these APIs in a central place.

In fact, smp_ barriers are stubs on !SMP, so they can be defined as follows:

arch/XXX/include/asm/barrier.h:

#define __smp_mb() DOSOMETHING

include/asm-generic/barrier.h:

#ifdef CONFIG_SMP
#define smp_mb() __smp_mb()
#else
#define smp_mb() barrier()
#endif

This has the benefit of cleaning out a bunch of duplicated
ifdefs on a bunch of architectures - this patchset brings
about a net reduction in LOC, more than compensated for
later by performance enhancements, extra documentation and tools :)

Then virt can use __smp_XXX when talking to an SMP host.
To make those users explicit, this patchset adds virt_xxx wrappers
for them.

Touching all archs is a tad tedious, but its fairly straight forward.

The patchset is structured as follows:


-. Patch 1 fixes a bug in asm-generic.
   It is already in tip, included here for completeness.

-. Patches 2-12 make sure barrier.h on all remaining
   architectures includes asm-generic/barrier.h:
   after the change in Patch 1, code there matches
   asm-generic/barrier.h almost verbatim.
   Minor code tweaks were required in a couple of places.
   Macros duplicated from asm-generic/barrier.h are dropped
   in the process.

After all that preparatory work, we are getting to the actual change.

-. Patch 13 adds generic smp_XXX wrappers in asm-generic:
   these select __smp_XXX or barrier() depending on CONFIG_SMP

-. Patches 14-27 change all architectures to
   define __smp_XXX macros; the generic code in asm-generic/barrier.h
   then defines smp_XXX macros

   I compiled the affected arches before and after the changes,
   dumped the .text section (using objdump -O binary) and
   made sure that the object code is exactly identical
   before and after the change.

   Note: the changes were intentionally done in a way
   that avoids generated code changes.
   When I got feedback from arch maintainers that the
   barriers can be improved, I made this in a separate
   patch on top, to allow this testing by binary comparisons.

Unfortunately, I don't have a metag cross-build toolset ready.
Hoping for some acks on this architecture.

Next, the following patches put the __smp_xxx APIs to work for virt:

-. Patch 28 adds virt_ wrappers for __smp_, and documents them.
   After all this work, this requires very few lines of code in
   the generic header.

-. Patches 29,30 convert virtio drivers to use the virt_xxx APIs
   tested on x86

-. Patches 31-33 teach virtio to use virt_store_mb
   sh architecture was missing a 2-byte xchg,
   needed for 2 byte smp_store_mb,
   so I had to add this support for sh

-. Patches 34-36 teach checkpatch to warn about
   misuse of the new barriers

-. Patches 37-39 convert xen drivers to use the virt_xxx APIs
   compiled only (by intel 0-day infrastructure)

-. Patch 40 makes some smp barriers on s390 more efficient
   included here to avoid merge conflicts, at maintainer's request

   tested on x86
Davidlohr Bueso (1):
  lcoking/barriers, arch: Use smp barriers in smp_store_release()

Michael S. Tsirkin (40):
  asm-generic: guard smp_store_release/load_acquire
  ia64: rename nop->iosapic_nop
  ia64: reuse asm-generic/barrier.h
  powerpc: reuse asm-generic/barrier.h
  s390: reuse asm-generic/barrier.h
  sparc: reuse asm-generic/barrier.h
  arm: reuse asm-generic/barrier.h
  arm64: reuse asm-generic/barrier.h
  metag: reuse asm-generic/barrier.h
  mips: reuse asm-generic/barrier.h
  x86/um: reuse asm-generic/barrier.h
  x86: reuse asm-generic/barrier.h
  asm-generic: add __smp_xxx wrappers
  powerpc: define __smp_xxx
  arm64: define __smp_xxx
  arm: define __smp_xxx
  blackfin: define __smp_xxx
  ia64: define __smp_xxx
  metag: define __smp_xxx
  mips: define __smp_xxx
  s390: define __smp_xxx
  sh: define __smp_xxx, fix smp_store_mb for !SMP
  sparc: define __smp_xxx
  tile: define __smp_xxx
  xtensa: define __smp_xxx
  x86: define __smp_xxx
  asm-generic: implement virt_xxx memory barriers
  Revert "virtio_ring: Update weak barriers to use dma_wmb/rmb"
  virtio_ring: update weak barriers to use virt_xxx
  sh: support 1 and 2 byte xchg
  sh: move xchg_cmpxchg to a header by itself
  virtio_ring: use virt_store_mb
  checkpatch.pl: add missing memory barriers
  checkpatch: check for __smp outside barrier.h
  checkpatch: add virt barriers
  xenbus: use virt_xxx barriers
  xen/io: use virt_xxx barriers
  xen/events: use virt_xxx barriers
  s390: use generic memory barriers
  s390: more efficient smp barriers

 arch/arm/include/asm/barrier.h      |  35 ++----------
 arch/arm64/include/asm/barrier.h    |  19 ++-----
 arch/blackfin/include/asm/barrier.h |   4 +-
 arch/ia64/include/asm/barrier.h     |  24 +++-----
 arch/metag/include/asm/barrier.h    |  55 ++++++-------------
 arch/mips/include/asm/barrier.h     |  51 ++++++-----------
 arch/powerpc/include/asm/barrier.h  |  33 ++++-------
 arch/s390/include/asm/barrier.h     |  23 ++++----
 arch/sh/include/asm/barrier.h       |   3 +-
 arch/sh/include/asm/cmpxchg-grb.h   |  22 ++++++++
 arch/sh/include/asm/cmpxchg-irq.h   |  11 ++++
 arch/sh/include/asm/cmpxchg-llsc.h  |  25 +--------
 arch/sh/include/asm/cmpxchg-xchg.h  |  51 +++++++++++++++++
 arch/sh/include/asm/cmpxchg.h       |   3 +
 arch/sparc/include/asm/barrier_32.h |   1 -
 arch/sparc/include/asm/barrier_64.h |  29 ++--------
 arch/sparc/include/asm/processor.h  |   3 -
 arch/tile/include/asm/barrier.h     |   9 +--
 arch/x86/include/asm/barrier.h      |  36 +++++-------
 arch/x86/um/asm/barrier.h           |   9 +--
 arch/xtensa/include/asm/barrier.h   |   4 +-
 include/asm-generic/barrier.h       | 106 +++++++++++++++++++++++++++++++++---
 include/linux/virtio_ring.h         |  21 +++++--
 include/xen/interface/io/ring.h     |  16 +++---
 arch/ia64/kernel/iosapic.c          |   6 +-
 drivers/virtio/virtio_ring.c        |  15 +++--
 drivers/xen/events/events_fifo.c    |   3 +-
 drivers/xen/xenbus/xenbus_comms.c   |   8 +--
 Documentation/memory-barriers.txt   |  28 ++++++++--
 scripts/checkpatch.pl               |  31 ++++++++++-
 30 files changed, 382 insertions(+), 302 deletions(-)
 create mode 100644 arch/sh/include/asm/cmpxchg-xchg.h

-- 
MST

From: Davidlohr Bueso <dave at stgolabs.net>

With commit b92b8b35a2e ("locking/arch: Rename set_mb() to
smp_store_mb()")
it was made clear that the context of this call (and thus set_mb)
is strictly for CPU ordering, as opposed to IO. As such all archs
should use the smp variant of mb(), respecting the semantics and
saving a mandatory barrier on UP.

Signed-off-by: Davidlohr Bueso <dbueso at suse.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz at infradead.org>
Cc: <linux-arch at vger.kernel.org>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
Cc: Heiko Carstens <heiko.carstens at de.ibm.com>
Cc: Linus Torvalds <torvalds at linux-foundation.org>
Cc: Paul E. McKenney <paulmck at linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Tony Luck <tony.luck at intel.com>
Cc: dave at stgolabs.net
Link: http://lkml.kernel.org/r/1445975631-17047-3-git-send-email-dave at
stgolabs.net
Signed-off-by: Ingo Molnar <mingo at kernel.org>
---
 arch/ia64/include/asm/barrier.h    | 2 +-
 arch/powerpc/include/asm/barrier.h | 2 +-
 arch/s390/include/asm/barrier.h    | 2 +-
 include/asm-generic/barrier.h      | 2 +-
 4 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/ia64/include/asm/barrier.h b/arch/ia64/include/asm/barrier.h
index df896a1..209c4b8 100644
--- a/arch/ia64/include/asm/barrier.h
+++ b/arch/ia64/include/asm/barrier.h
@@ -77,7 +77,7 @@ do {									\
 	___p1;								\
 })
 
-#define smp_store_mb(var, value)	do { WRITE_ONCE(var, value); mb(); } while (0)
+#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } while
(0)
 
 /*
  * The group barrier in front of the rsm & ssm are necessary to ensure
diff --git a/arch/powerpc/include/asm/barrier.h
b/arch/powerpc/include/asm/barrier.h
index 0eca6ef..a7af5fb 100644
--- a/arch/powerpc/include/asm/barrier.h
+++ b/arch/powerpc/include/asm/barrier.h
@@ -34,7 +34,7 @@
 #define rmb()  __asm__ __volatile__ ("sync" : : : "memory")
 #define wmb()  __asm__ __volatile__ ("sync" : : : "memory")
 
-#define smp_store_mb(var, value)	do { WRITE_ONCE(var, value); mb(); } while (0)
+#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } while
(0)
 
 #ifdef __SUBARCH_HAS_LWSYNC
 #    define SMPWMB      LWSYNC
diff --git a/arch/s390/include/asm/barrier.h b/arch/s390/include/asm/barrier.h
index d68e11e..7ffd0b1 100644
--- a/arch/s390/include/asm/barrier.h
+++ b/arch/s390/include/asm/barrier.h
@@ -36,7 +36,7 @@
 #define smp_mb__before_atomic()		smp_mb()
 #define smp_mb__after_atomic()		smp_mb()
 
-#define smp_store_mb(var, value)		do { WRITE_ONCE(var, value); mb(); } while
(0)
+#define smp_store_mb(var, value)	do { WRITE_ONCE(var, value); smp_mb(); } while
(0)
 
 #define smp_store_release(p, v)						\
 do {									\
diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
index b42afad..0f45f93 100644
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -93,7 +93,7 @@
 #endif	/* CONFIG_SMP */
 
 #ifndef smp_store_mb
-#define smp_store_mb(var, value)  do { WRITE_ONCE(var, value); mb(); } while
(0)
+#define smp_store_mb(var, value)  do { WRITE_ONCE(var, value); smp_mb(); }
while (0)
 #endif
 
 #ifndef smp_mb__before_atomic
-- 
MST

Allow architectures to override smp_store_release
and smp_load_acquire by guarding the defines
in asm-generic/barrier.h with ifndef directives.

This is in preparation to reusing asm-generic/barrier.h
on architectures which have their own definition
of these macros.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
---
 include/asm-generic/barrier.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
index 0f45f93..987b2e0 100644
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -104,13 +104,16 @@
 #define smp_mb__after_atomic()	smp_mb()
 #endif
 
+#ifndef smp_store_release
 #define smp_store_release(p, v)						\
 do {									\
 	compiletime_assert_atomic_type(*p);				\
 	smp_mb();							\
 	WRITE_ONCE(*p, v);						\
 } while (0)
+#endif
 
+#ifndef smp_load_acquire
 #define smp_load_acquire(p)						\
 ({									\
 	typeof(*p) ___p1 = READ_ONCE(*p);				\
@@ -118,6 +121,7 @@ do {									\
 	smp_mb();							\
 	___p1;								\
 })
+#endif
 
 #endif /* !__ASSEMBLY__ */
 #endif /* __ASM_GENERIC_BARRIER_H */
-- 
MST

asm-generic/barrier.h defines a nop() macro.
To be able to use this header on ia64, we shouldn't
call local functions/variables nop().

There's one instance where this breaks on ia64:
rename the function to iosapic_nop to avoid the conflict.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Tony Luck <tony.luck at intel.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
---
 arch/ia64/kernel/iosapic.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/ia64/kernel/iosapic.c b/arch/ia64/kernel/iosapic.c
index d2fae05..90fde5b 100644
--- a/arch/ia64/kernel/iosapic.c
+++ b/arch/ia64/kernel/iosapic.c
@@ -256,7 +256,7 @@ set_rte (unsigned int gsi, unsigned int irq, unsigned int
dest, int mask)
 }
 
 static void
-nop (struct irq_data *data)
+iosapic_nop (struct irq_data *data)
 {
 	/* do nothing... */
 }
@@ -415,7 +415,7 @@ iosapic_unmask_level_irq (struct irq_data *data)
 #define iosapic_shutdown_level_irq	mask_irq
 #define iosapic_enable_level_irq	unmask_irq
 #define iosapic_disable_level_irq	mask_irq
-#define iosapic_ack_level_irq		nop
+#define iosapic_ack_level_irq		iosapic_nop
 
 static struct irq_chip irq_type_iosapic_level = {
 	.name =			"IO-SAPIC-level",
@@ -453,7 +453,7 @@ iosapic_ack_edge_irq (struct irq_data *data)
 }
 
 #define iosapic_enable_edge_irq		unmask_irq
-#define iosapic_disable_edge_irq	nop
+#define iosapic_disable_edge_irq	iosapic_nop
 
 static struct irq_chip irq_type_iosapic_edge = {
 	.name =			"IO-SAPIC-edge",
-- 
MST

On ia64 smp_rmb, smp_wmb, read_barrier_depends, smp_read_barrier_depends
and smp_store_mb() match the asm-generic variants exactly. Drop the
local definitions and pull in asm-generic/barrier.h instead.

This is in preparation to refactoring this code area.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Tony Luck <tony.luck at intel.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
---
 arch/ia64/include/asm/barrier.h | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/arch/ia64/include/asm/barrier.h b/arch/ia64/include/asm/barrier.h
index 209c4b8..2f93348 100644
--- a/arch/ia64/include/asm/barrier.h
+++ b/arch/ia64/include/asm/barrier.h
@@ -48,12 +48,6 @@
 # define smp_mb()	barrier()
 #endif
 
-#define smp_rmb()	smp_mb()
-#define smp_wmb()	smp_mb()
-
-#define read_barrier_depends()		do { } while (0)
-#define smp_read_barrier_depends()	do { } while (0)
-
 #define smp_mb__before_atomic()	barrier()
 #define smp_mb__after_atomic()	barrier()
 
@@ -77,12 +71,12 @@ do {									\
 	___p1;								\
 })
 
-#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } while
(0)
-
 /*
  * The group barrier in front of the rsm & ssm are necessary to ensure
  * that none of the previous instructions in the same group are
  * affected by the rsm/ssm.
  */
 
+#include <asm-generic/barrier.h>
+
 #endif /* _ASM_IA64_BARRIER_H */
-- 
MST

On powerpc read_barrier_depends, smp_read_barrier_depends
smp_store_mb(), smp_mb__before_atomic and smp_mb__after_atomic match the
asm-generic variants exactly. Drop the local definitions and pull in
asm-generic/barrier.h instead.

This is in preparation to refactoring this code area.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
---
 arch/powerpc/include/asm/barrier.h | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/arch/powerpc/include/asm/barrier.h
b/arch/powerpc/include/asm/barrier.h
index a7af5fb..980ad0c 100644
--- a/arch/powerpc/include/asm/barrier.h
+++ b/arch/powerpc/include/asm/barrier.h
@@ -34,8 +34,6 @@
 #define rmb()  __asm__ __volatile__ ("sync" : : : "memory")
 #define wmb()  __asm__ __volatile__ ("sync" : : : "memory")
 
-#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } while
(0)
-
 #ifdef __SUBARCH_HAS_LWSYNC
 #    define SMPWMB      LWSYNC
 #else
@@ -60,9 +58,6 @@
 #define smp_wmb()	barrier()
 #endif /* CONFIG_SMP */
 
-#define read_barrier_depends()		do { } while (0)
-#define smp_read_barrier_depends()	do { } while (0)
-
 /*
  * This is a barrier which prevents following instructions from being
  * started until the value of the argument x is known.  For example, if
@@ -87,8 +82,8 @@ do {									\
 	___p1;								\
 })
 
-#define smp_mb__before_atomic()     smp_mb()
-#define smp_mb__after_atomic()      smp_mb()
 #define smp_mb__before_spinlock()   smp_mb()
 
+#include <asm-generic/barrier.h>
+
 #endif /* _ASM_POWERPC_BARRIER_H */
-- 
MST

On s390 read_barrier_depends, smp_read_barrier_depends
smp_store_mb(), smp_mb__before_atomic and smp_mb__after_atomic match the
asm-generic variants exactly. Drop the local definitions and pull in
asm-generic/barrier.h instead.

This is in preparation to refactoring this code area.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
---
 arch/s390/include/asm/barrier.h | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/arch/s390/include/asm/barrier.h b/arch/s390/include/asm/barrier.h
index 7ffd0b1..c358c31 100644
--- a/arch/s390/include/asm/barrier.h
+++ b/arch/s390/include/asm/barrier.h
@@ -30,14 +30,6 @@
 #define smp_rmb()			rmb()
 #define smp_wmb()			wmb()
 
-#define read_barrier_depends()		do { } while (0)
-#define smp_read_barrier_depends()	do { } while (0)
-
-#define smp_mb__before_atomic()		smp_mb()
-#define smp_mb__after_atomic()		smp_mb()
-
-#define smp_store_mb(var, value)	do { WRITE_ONCE(var, value); smp_mb(); } while
(0)
-
 #define smp_store_release(p, v)						\
 do {									\
 	compiletime_assert_atomic_type(*p);				\
@@ -53,4 +45,6 @@ do {									\
 	___p1;								\
 })
 
+#include <asm-generic/barrier.h>
+
 #endif /* __ASM_BARRIER_H */
-- 
MST

On sparc 64 bit dma_rmb, dma_wmb, smp_store_mb, smp_mb, smp_rmb,
smp_wmb, read_barrier_depends and smp_read_barrier_depends match the
asm-generic variants exactly. Drop the local definitions and pull in
asm-generic/barrier.h instead.

nop uses __asm__ __volatile but is otherwise identical to
the generic version, drop that as well.

This is in preparation to refactoring this code area.

Note: nop() was in processor.h and not in barrier.h as on other
architectures. Nothing seems to depend on it being there though.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
Acked-by: David S. Miller <davem at davemloft.net>
---
 arch/sparc/include/asm/barrier_32.h |  1 -
 arch/sparc/include/asm/barrier_64.h | 21 ++-------------------
 arch/sparc/include/asm/processor.h  |  3 ---
 3 files changed, 2 insertions(+), 23 deletions(-)

diff --git a/arch/sparc/include/asm/barrier_32.h
b/arch/sparc/include/asm/barrier_32.h
index ae69eda..8059130 100644
--- a/arch/sparc/include/asm/barrier_32.h
+++ b/arch/sparc/include/asm/barrier_32.h
@@ -1,7 +1,6 @@
 #ifndef __SPARC_BARRIER_H
 #define __SPARC_BARRIER_H
 
-#include <asm/processor.h> /* for nop() */
 #include <asm-generic/barrier.h>
 
 #endif /* !(__SPARC_BARRIER_H) */
diff --git a/arch/sparc/include/asm/barrier_64.h
b/arch/sparc/include/asm/barrier_64.h
index 14a9286..26c3f72 100644
--- a/arch/sparc/include/asm/barrier_64.h
+++ b/arch/sparc/include/asm/barrier_64.h
@@ -37,25 +37,6 @@ do {	__asm__ __volatile__("ba,pt	%%xcc, 1f\n\t" \
 #define rmb()	__asm__ __volatile__("":::"memory")
 #define wmb()	__asm__ __volatile__("":::"memory")
 
-#define dma_rmb()	rmb()
-#define dma_wmb()	wmb()
-
-#define smp_store_mb(__var, __value) \
-	do { WRITE_ONCE(__var, __value); membar_safe("#StoreLoad"); }
while(0)
-
-#ifdef CONFIG_SMP
-#define smp_mb()	mb()
-#define smp_rmb()	rmb()
-#define smp_wmb()	wmb()
-#else
-#define smp_mb()	__asm__ __volatile__("":::"memory")
-#define smp_rmb()	__asm__ __volatile__("":::"memory")
-#define smp_wmb()	__asm__ __volatile__("":::"memory")
-#endif
-
-#define read_barrier_depends()		do { } while (0)
-#define smp_read_barrier_depends()	do { } while (0)
-
 #define smp_store_release(p, v)						\
 do {									\
 	compiletime_assert_atomic_type(*p);				\
@@ -74,4 +55,6 @@ do {									\
 #define smp_mb__before_atomic()	barrier()
 #define smp_mb__after_atomic()	barrier()
 
+#include <asm-generic/barrier.h>
+
 #endif /* !(__SPARC64_BARRIER_H) */
diff --git a/arch/sparc/include/asm/processor.h
b/arch/sparc/include/asm/processor.h
index 2fe99e6..9da9646 100644
--- a/arch/sparc/include/asm/processor.h
+++ b/arch/sparc/include/asm/processor.h
@@ -5,7 +5,4 @@
 #else
 #include <asm/processor_32.h>
 #endif
-
-#define nop() 		__asm__ __volatile__ ("nop")
-
 #endif
-- 
MST

On arm smp_store_mb, read_barrier_depends, smp_read_barrier_depends,
smp_store_release, smp_load_acquire, smp_mb__before_atomic and
smp_mb__after_atomic match the asm-generic variants exactly. Drop the
local definitions and pull in asm-generic/barrier.h instead.

This is in preparation to refactoring this code area.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
Acked-by: Russell King <rmk+kernel at arm.linux.org.uk>
---
 arch/arm/include/asm/barrier.h | 23 +----------------------
 1 file changed, 1 insertion(+), 22 deletions(-)

diff --git a/arch/arm/include/asm/barrier.h b/arch/arm/include/asm/barrier.h
index 3ff5642..31152e8 100644
--- a/arch/arm/include/asm/barrier.h
+++ b/arch/arm/include/asm/barrier.h
@@ -70,28 +70,7 @@ extern void arm_heavy_mb(void);
 #define smp_wmb()	dmb(ishst)
 #endif
 
-#define smp_store_release(p, v)						\
-do {									\
-	compiletime_assert_atomic_type(*p);				\
-	smp_mb();							\
-	WRITE_ONCE(*p, v);						\
-} while (0)
-
-#define smp_load_acquire(p)						\
-({									\
-	typeof(*p) ___p1 = READ_ONCE(*p);				\
-	compiletime_assert_atomic_type(*p);				\
-	smp_mb();							\
-	___p1;								\
-})
-
-#define read_barrier_depends()		do { } while(0)
-#define smp_read_barrier_depends()	do { } while(0)
-
-#define smp_store_mb(var, value)	do { WRITE_ONCE(var, value); smp_mb(); } while
(0)
-
-#define smp_mb__before_atomic()	smp_mb()
-#define smp_mb__after_atomic()	smp_mb()
+#include <asm-generic/barrier.h>
 
 #endif /* !__ASSEMBLY__ */
 #endif /* __ASM_BARRIER_H */
-- 
MST

On arm64 nop, read_barrier_depends, smp_read_barrier_depends
smp_store_mb(), smp_mb__before_atomic and smp_mb__after_atomic match the
asm-generic variants exactly. Drop the local definitions and pull in
asm-generic/barrier.h instead.

This is in preparation to refactoring this code area.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
---
 arch/arm64/include/asm/barrier.h | 9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h
index 9622eb4..91a43f4 100644
--- a/arch/arm64/include/asm/barrier.h
+++ b/arch/arm64/include/asm/barrier.h
@@ -91,14 +91,7 @@ do {									\
 	__u.__val;							\
 })
 
-#define read_barrier_depends()		do { } while(0)
-#define smp_read_barrier_depends()	do { } while(0)
-
-#define smp_store_mb(var, value)	do { WRITE_ONCE(var, value); smp_mb(); } while
(0)
-#define nop()		asm volatile("nop");
-
-#define smp_mb__before_atomic()	smp_mb()
-#define smp_mb__after_atomic()	smp_mb()
+#include <asm-generic/barrier.h>
 
 #endif	/* __ASSEMBLY__ */
 
-- 
MST

On metag dma_rmb, dma_wmb, smp_store_mb, read_barrier_depends,
smp_read_barrier_depends, smp_store_release and smp_load_acquire  match
the asm-generic variants exactly. Drop the local definitions and pull in
asm-generic/barrier.h instead.

This is in preparation to refactoring this code area.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
---
 arch/metag/include/asm/barrier.h | 25 ++-----------------------
 1 file changed, 2 insertions(+), 23 deletions(-)

diff --git a/arch/metag/include/asm/barrier.h b/arch/metag/include/asm/barrier.h
index 172b7e5..b5b778b 100644
--- a/arch/metag/include/asm/barrier.h
+++ b/arch/metag/include/asm/barrier.h
@@ -44,9 +44,6 @@ static inline void wr_fence(void)
 #define rmb()		barrier()
 #define wmb()		mb()
 
-#define dma_rmb()	rmb()
-#define dma_wmb()	wmb()
-
 #ifndef CONFIG_SMP
 #define fence()		do { } while (0)
 #define smp_mb()        barrier()
@@ -81,27 +78,9 @@ static inline void fence(void)
 #endif
 #endif
 
-#define read_barrier_depends()		do { } while (0)
-#define smp_read_barrier_depends()	do { } while (0)
-
-#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); } while
(0)
-
-#define smp_store_release(p, v)						\
-do {									\
-	compiletime_assert_atomic_type(*p);				\
-	smp_mb();							\
-	WRITE_ONCE(*p, v);						\
-} while (0)
-
-#define smp_load_acquire(p)						\
-({									\
-	typeof(*p) ___p1 = READ_ONCE(*p);				\
-	compiletime_assert_atomic_type(*p);				\
-	smp_mb();							\
-	___p1;								\
-})
-
 #define smp_mb__before_atomic()	barrier()
 #define smp_mb__after_atomic()	barrier()
 
+#include <asm-generic/barrier.h>
+
 #endif /* _ASM_METAG_BARRIER_H */
-- 
MST

On mips dma_rmb, dma_wmb, smp_store_mb, read_barrier_depends,
smp_read_barrier_depends, smp_store_release and smp_load_acquire  match
the asm-generic variants exactly. Drop the local definitions and pull in
asm-generic/barrier.h instead.

This is in preparation to refactoring this code area.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
---
 arch/mips/include/asm/barrier.h | 25 ++-----------------------
 1 file changed, 2 insertions(+), 23 deletions(-)

diff --git a/arch/mips/include/asm/barrier.h b/arch/mips/include/asm/barrier.h
index 752e0b8..3eac4b9 100644
--- a/arch/mips/include/asm/barrier.h
+++ b/arch/mips/include/asm/barrier.h
@@ -10,9 +10,6 @@
 
 #include <asm/addrspace.h>
 
-#define read_barrier_depends()		do { } while(0)
-#define smp_read_barrier_depends()	do { } while(0)
-
 #ifdef CONFIG_CPU_HAS_SYNC
 #define __sync()				\
 	__asm__ __volatile__(			\
@@ -87,8 +84,6 @@
 
 #define wmb()		fast_wmb()
 #define rmb()		fast_rmb()
-#define dma_wmb()	fast_wmb()
-#define dma_rmb()	fast_rmb()
 
 #if defined(CONFIG_WEAK_ORDERING) && defined(CONFIG_SMP)
 # ifdef CONFIG_CPU_CAVIUM_OCTEON
@@ -112,9 +107,6 @@
 #define __WEAK_LLSC_MB		"		\n"
 #endif
 
-#define smp_store_mb(var, value) \
-	do { WRITE_ONCE(var, value); smp_mb(); } while (0)
-
 #define smp_llsc_mb()	__asm__ __volatile__(__WEAK_LLSC_MB : :
:"memory")
 
 #ifdef CONFIG_CPU_CAVIUM_OCTEON
@@ -129,22 +121,9 @@
 #define nudge_writes() mb()
 #endif
 
-#define smp_store_release(p, v)						\
-do {									\
-	compiletime_assert_atomic_type(*p);				\
-	smp_mb();							\
-	WRITE_ONCE(*p, v);						\
-} while (0)
-
-#define smp_load_acquire(p)						\
-({									\
-	typeof(*p) ___p1 = READ_ONCE(*p);				\
-	compiletime_assert_atomic_type(*p);				\
-	smp_mb();							\
-	___p1;								\
-})
-
 #define smp_mb__before_atomic()	smp_mb__before_llsc()
 #define smp_mb__after_atomic()	smp_llsc_mb()
 
+#include <asm-generic/barrier.h>
+
 #endif /* __ASM_BARRIER_H */
-- 
MST

On x86/um CONFIG_SMP is never defined.  As a result, several macros
match the asm-generic variant exactly. Drop the local definitions and
pull in asm-generic/barrier.h instead.

This is in preparation to refactoring this code area.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
Acked-by: Richard Weinberger <richard at nod.at>
---
 arch/x86/um/asm/barrier.h | 9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/arch/x86/um/asm/barrier.h b/arch/x86/um/asm/barrier.h
index 755481f..174781a 100644
--- a/arch/x86/um/asm/barrier.h
+++ b/arch/x86/um/asm/barrier.h
@@ -36,13 +36,6 @@
 #endif /* CONFIG_X86_PPRO_FENCE */
 #define dma_wmb()	barrier()
 
-#define smp_mb()	barrier()
-#define smp_rmb()	barrier()
-#define smp_wmb()	barrier()
-
-#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); barrier(); }
while (0)
-
-#define read_barrier_depends()		do { } while (0)
-#define smp_read_barrier_depends()	do { } while (0)
+#include <asm-generic/barrier.h>
 
 #endif
-- 
MST

As on most architectures, on x86 read_barrier_depends and
smp_read_barrier_depends are empty.  Drop the local definitions and pull
the generic ones from asm-generic/barrier.h instead: they are identical.

This is in preparation to refactoring this code area.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
---
 arch/x86/include/asm/barrier.h | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/barrier.h b/arch/x86/include/asm/barrier.h
index 0681d25..cc4c2a7 100644
--- a/arch/x86/include/asm/barrier.h
+++ b/arch/x86/include/asm/barrier.h
@@ -43,9 +43,6 @@
 #define smp_store_mb(var, value) do { WRITE_ONCE(var, value); barrier(); }
while (0)
 #endif /* SMP */
 
-#define read_barrier_depends()		do { } while (0)
-#define smp_read_barrier_depends()	do { } while (0)
-
 #if defined(CONFIG_X86_PPRO_FENCE)
 
 /*
@@ -91,4 +88,6 @@ do {									\
 #define smp_mb__before_atomic()	barrier()
 #define smp_mb__after_atomic()	barrier()
 
+#include <asm-generic/barrier.h>
+
 #endif /* _ASM_X86_BARRIER_H */
-- 
MST

On !SMP, most architectures define their
barriers as compiler barriers.
On SMP, most need an actual barrier.

Make it possible to remove the code duplication for
!SMP by defining low-level __smp_xxx barriers
which do not depend on the value of SMP, then
use them from asm-generic conditionally.

Besides reducing code duplication, these low level APIs will also be
useful for virtualization, where a barrier is sometimes needed even if
!SMP since we might be talking to another kernel on the same SMP system.

Both virtio and Xen drivers will benefit.

The smp_xxx variants should use __smp_XXX ones or barrier() depending on
SMP, identically for all architectures.

We keep ifndef guards around them for now - once/if all
architectures are converted to use the generic
code, we'll be able to remove these.

Suggested-by: Peter Zijlstra <peterz at infradead.org>
Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
---
 include/asm-generic/barrier.h | 91 ++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 82 insertions(+), 9 deletions(-)

diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
index 987b2e0..8752964 100644
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -54,22 +54,38 @@
 #define read_barrier_depends()		do { } while (0)
 #endif
 
+#ifndef __smp_mb
+#define __smp_mb()	mb()
+#endif
+
+#ifndef __smp_rmb
+#define __smp_rmb()	rmb()
+#endif
+
+#ifndef __smp_wmb
+#define __smp_wmb()	wmb()
+#endif
+
+#ifndef __smp_read_barrier_depends
+#define __smp_read_barrier_depends()	read_barrier_depends()
+#endif
+
 #ifdef CONFIG_SMP
 
 #ifndef smp_mb
-#define smp_mb()	mb()
+#define smp_mb()	__smp_mb()
 #endif
 
 #ifndef smp_rmb
-#define smp_rmb()	rmb()
+#define smp_rmb()	__smp_rmb()
 #endif
 
 #ifndef smp_wmb
-#define smp_wmb()	wmb()
+#define smp_wmb()	__smp_wmb()
 #endif
 
 #ifndef smp_read_barrier_depends
-#define smp_read_barrier_depends()	read_barrier_depends()
+#define smp_read_barrier_depends()	__smp_read_barrier_depends()
 #endif
 
 #else	/* !CONFIG_SMP */
@@ -92,23 +108,78 @@
 
 #endif	/* CONFIG_SMP */
 
+#ifndef __smp_store_mb
+#define __smp_store_mb(var, value)  do { WRITE_ONCE(var, value); __smp_mb(); }
while (0)
+#endif
+
+#ifndef __smp_mb__before_atomic
+#define __smp_mb__before_atomic()	__smp_mb()
+#endif
+
+#ifndef __smp_mb__after_atomic
+#define __smp_mb__after_atomic()	__smp_mb()
+#endif
+
+#ifndef __smp_store_release
+#define __smp_store_release(p, v)					\
+do {									\
+	compiletime_assert_atomic_type(*p);				\
+	__smp_mb();							\
+	WRITE_ONCE(*p, v);						\
+} while (0)
+#endif
+
+#ifndef __smp_load_acquire
+#define __smp_load_acquire(p)						\
+({									\
+	typeof(*p) ___p1 = READ_ONCE(*p);				\
+	compiletime_assert_atomic_type(*p);				\
+	__smp_mb();							\
+	___p1;								\
+})
+#endif
+
+#ifdef CONFIG_SMP
+
+#ifndef smp_store_mb
+#define smp_store_mb(var, value)  __smp_store_mb(var, value)
+#endif
+
+#ifndef smp_mb__before_atomic
+#define smp_mb__before_atomic()	__smp_mb__before_atomic()
+#endif
+
+#ifndef smp_mb__after_atomic
+#define smp_mb__after_atomic()	__smp_mb__after_atomic()
+#endif
+
+#ifndef smp_store_release
+#define smp_store_release(p, v) __smp_store_release(p, v)
+#endif
+
+#ifndef smp_load_acquire
+#define smp_load_acquire(p) __smp_load_acquire(p)
+#endif
+
+#else	/* !CONFIG_SMP */
+
 #ifndef smp_store_mb
-#define smp_store_mb(var, value)  do { WRITE_ONCE(var, value); smp_mb(); }
while (0)
+#define smp_store_mb(var, value)  do { WRITE_ONCE(var, value); barrier(); }
while (0)
 #endif
 
 #ifndef smp_mb__before_atomic
-#define smp_mb__before_atomic()	smp_mb()
+#define smp_mb__before_atomic()	barrier()
 #endif
 
 #ifndef smp_mb__after_atomic
-#define smp_mb__after_atomic()	smp_mb()
+#define smp_mb__after_atomic()	barrier()
 #endif
 
 #ifndef smp_store_release
 #define smp_store_release(p, v)						\
 do {									\
 	compiletime_assert_atomic_type(*p);				\
-	smp_mb();							\
+	barrier();							\
 	WRITE_ONCE(*p, v);						\
 } while (0)
 #endif
@@ -118,10 +189,12 @@ do {									\
 ({									\
 	typeof(*p) ___p1 = READ_ONCE(*p);				\
 	compiletime_assert_atomic_type(*p);				\
-	smp_mb();							\
+	barrier();							\
 	___p1;								\
 })
 #endif
 
+#endif
+
 #endif /* !__ASSEMBLY__ */
 #endif /* __ASM_GENERIC_BARRIER_H */
-- 
MST

This defines __smp_xxx barriers for powerpc
for use by virtualization.

smp_xxx barriers are removed as they are
defined correctly by asm-generic/barriers.h

This reduces the amount of arch-specific boiler-plate code.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
Acked-by: Boqun Feng <boqun.feng at gmail.com>
---
 arch/powerpc/include/asm/barrier.h | 24 ++++++++----------------
 1 file changed, 8 insertions(+), 16 deletions(-)

diff --git a/arch/powerpc/include/asm/barrier.h
b/arch/powerpc/include/asm/barrier.h
index 980ad0c..c0deafc 100644
--- a/arch/powerpc/include/asm/barrier.h
+++ b/arch/powerpc/include/asm/barrier.h
@@ -44,19 +44,11 @@
 #define dma_rmb()	__lwsync()
 #define dma_wmb()	__asm__ __volatile__ (stringify_in_c(SMPWMB) : :
:"memory")
 
-#ifdef CONFIG_SMP
-#define smp_lwsync()	__lwsync()
+#define __smp_lwsync()	__lwsync()
 
-#define smp_mb()	mb()
-#define smp_rmb()	__lwsync()
-#define smp_wmb()	__asm__ __volatile__ (stringify_in_c(SMPWMB) : :
:"memory")
-#else
-#define smp_lwsync()	barrier()
-
-#define smp_mb()	barrier()
-#define smp_rmb()	barrier()
-#define smp_wmb()	barrier()
-#endif /* CONFIG_SMP */
+#define __smp_mb()	mb()
+#define __smp_rmb()	__lwsync()
+#define __smp_wmb()	__asm__ __volatile__ (stringify_in_c(SMPWMB) : :
:"memory")
 
 /*
  * This is a barrier which prevents following instructions from being
@@ -67,18 +59,18 @@
 #define data_barrier(x)	\
 	asm volatile("twi 0,%0,0; isync" : : "r" (x) :
"memory");
 
-#define smp_store_release(p, v)						\
+#define __smp_store_release(p, v)						\
 do {									\
 	compiletime_assert_atomic_type(*p);				\
-	smp_lwsync();							\
+	__smp_lwsync();							\
 	WRITE_ONCE(*p, v);						\
 } while (0)
 
-#define smp_load_acquire(p)						\
+#define __smp_load_acquire(p)						\
 ({									\
 	typeof(*p) ___p1 = READ_ONCE(*p);				\
 	compiletime_assert_atomic_type(*p);				\
-	smp_lwsync();							\
+	__smp_lwsync();							\
 	___p1;								\
 })
 
-- 
MST

This defines __smp_xxx barriers for arm64,
for use by virtualization.

smp_xxx barriers are removed as they are
defined correctly by asm-generic/barriers.h

Note: arm64 does not support !SMP config,
so smp_xxx and __smp_xxx are always equivalent.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
---
 arch/arm64/include/asm/barrier.h | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h
index 91a43f4..dae5c49 100644
--- a/arch/arm64/include/asm/barrier.h
+++ b/arch/arm64/include/asm/barrier.h
@@ -35,11 +35,11 @@
 #define dma_rmb()	dmb(oshld)
 #define dma_wmb()	dmb(oshst)
 
-#define smp_mb()	dmb(ish)
-#define smp_rmb()	dmb(ishld)
-#define smp_wmb()	dmb(ishst)
+#define __smp_mb()	dmb(ish)
+#define __smp_rmb()	dmb(ishld)
+#define __smp_wmb()	dmb(ishst)
 
-#define smp_store_release(p, v)						\
+#define __smp_store_release(p, v)						\
 do {									\
 	compiletime_assert_atomic_type(*p);				\
 	switch (sizeof(*p)) {						\
@@ -62,7 +62,7 @@ do {									\
 	}								\
 } while (0)
 
-#define smp_load_acquire(p)						\
+#define __smp_load_acquire(p)						\
 ({									\
 	union { typeof(*p) __val; char __c[1]; } __u;			\
 	compiletime_assert_atomic_type(*p);				\
-- 
MST

This defines __smp_xxx barriers for arm,
for use by virtualization.

smp_xxx barriers are removed as they are
defined correctly by asm-generic/barriers.h

This reduces the amount of arch-specific boiler-plate code.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
Acked-by: Russell King <rmk+kernel at arm.linux.org.uk>
---
 arch/arm/include/asm/barrier.h | 12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)

diff --git a/arch/arm/include/asm/barrier.h b/arch/arm/include/asm/barrier.h
index 31152e8..112cc1a 100644
--- a/arch/arm/include/asm/barrier.h
+++ b/arch/arm/include/asm/barrier.h
@@ -60,15 +60,9 @@ extern void arm_heavy_mb(void);
 #define dma_wmb()	barrier()
 #endif
 
-#ifndef CONFIG_SMP
-#define smp_mb()	barrier()
-#define smp_rmb()	barrier()
-#define smp_wmb()	barrier()
-#else
-#define smp_mb()	dmb(ish)
-#define smp_rmb()	smp_mb()
-#define smp_wmb()	dmb(ishst)
-#endif
+#define __smp_mb()	dmb(ish)
+#define __smp_rmb()	__smp_mb()
+#define __smp_wmb()	dmb(ishst)
 
 #include <asm-generic/barrier.h>
 
-- 
MST

This defines __smp_xxx barriers for blackfin,
for use by virtualization.

smp_xxx barriers are removed as they are
defined correctly by asm-generic/barriers.h

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
---
 arch/blackfin/include/asm/barrier.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/blackfin/include/asm/barrier.h
b/arch/blackfin/include/asm/barrier.h
index dfb66fe..7cca51c 100644
--- a/arch/blackfin/include/asm/barrier.h
+++ b/arch/blackfin/include/asm/barrier.h
@@ -78,8 +78,8 @@
 
 #endif /* !CONFIG_SMP */
 
-#define smp_mb__before_atomic()	barrier()
-#define smp_mb__after_atomic()	barrier()
+#define __smp_mb__before_atomic()	barrier()
+#define __smp_mb__after_atomic()	barrier()
 
 #include <asm-generic/barrier.h>
 
-- 
MST

This defines __smp_xxx barriers for ia64,
for use by virtualization.

smp_xxx barriers are removed as they are
defined correctly by asm-generic/barriers.h

This reduces the amount of arch-specific boiler-plate code.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Tony Luck <tony.luck at intel.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
---
 arch/ia64/include/asm/barrier.h | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/arch/ia64/include/asm/barrier.h b/arch/ia64/include/asm/barrier.h
index 2f93348..588f161 100644
--- a/arch/ia64/include/asm/barrier.h
+++ b/arch/ia64/include/asm/barrier.h
@@ -42,28 +42,24 @@
 #define dma_rmb()	mb()
 #define dma_wmb()	mb()
 
-#ifdef CONFIG_SMP
-# define smp_mb()	mb()
-#else
-# define smp_mb()	barrier()
-#endif
+# define __smp_mb()	mb()
 
-#define smp_mb__before_atomic()	barrier()
-#define smp_mb__after_atomic()	barrier()
+#define __smp_mb__before_atomic()	barrier()
+#define __smp_mb__after_atomic()	barrier()
 
 /*
  * IA64 GCC turns volatile stores into st.rel and volatile loads into ld.acq no
  * need for asm trickery!
  */
 
-#define smp_store_release(p, v)						\
+#define __smp_store_release(p, v)						\
 do {									\
 	compiletime_assert_atomic_type(*p);				\
 	barrier();							\
 	WRITE_ONCE(*p, v);						\
 } while (0)
 
-#define smp_load_acquire(p)						\
+#define __smp_load_acquire(p)						\
 ({									\
 	typeof(*p) ___p1 = READ_ONCE(*p);				\
 	compiletime_assert_atomic_type(*p);				\
-- 
MST

This defines __smp_xxx barriers for metag,
for use by virtualization.

smp_xxx barriers are removed as they are
defined correctly by asm-generic/barriers.h

Note: as __smp_XX macros should not depend on CONFIG_SMP, they can not
use the existing fence() macro since that is defined differently between
SMP and !SMP.  For this reason, this patch introduces a wrapper
metag_fence() that doesn't depend on CONFIG_SMP.
fence() is then defined using that, depending on CONFIG_SMP.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
---
 arch/metag/include/asm/barrier.h | 32 +++++++++++++++-----------------
 1 file changed, 15 insertions(+), 17 deletions(-)

diff --git a/arch/metag/include/asm/barrier.h b/arch/metag/include/asm/barrier.h
index b5b778b..84880c9 100644
--- a/arch/metag/include/asm/barrier.h
+++ b/arch/metag/include/asm/barrier.h
@@ -44,13 +44,6 @@ static inline void wr_fence(void)
 #define rmb()		barrier()
 #define wmb()		mb()
 
-#ifndef CONFIG_SMP
-#define fence()		do { } while (0)
-#define smp_mb()        barrier()
-#define smp_rmb()       barrier()
-#define smp_wmb()       barrier()
-#else
-
 #ifdef CONFIG_METAG_SMP_WRITE_REORDERING
 /*
  * Write to the atomic memory unlock system event register (command 0). This is
@@ -60,26 +53,31 @@ static inline void wr_fence(void)
  * incoherence). It is therefore ineffective if used after and on the same
  * thread as a write.
  */
-static inline void fence(void)
+static inline void metag_fence(void)
 {
 	volatile int *flushptr = (volatile int *) LINSYSEVENT_WR_ATOMIC_UNLOCK;
 	barrier();
 	*flushptr = 0;
 	barrier();
 }
-#define smp_mb()        fence()
-#define smp_rmb()       fence()
-#define smp_wmb()       barrier()
+#define __smp_mb()        metag_fence()
+#define __smp_rmb()       metag_fence()
+#define __smp_wmb()       barrier()
 #else
-#define fence()		do { } while (0)
-#define smp_mb()        barrier()
-#define smp_rmb()       barrier()
-#define smp_wmb()       barrier()
+#define metag_fence()		do { } while (0)
+#define __smp_mb()        barrier()
+#define __smp_rmb()       barrier()
+#define __smp_wmb()       barrier()
 #endif
+
+#ifdef CONFIG_SMP
+#define fence() metag_fence()
+#else
+#define fence()		do { } while (0)
 #endif
 
-#define smp_mb__before_atomic()	barrier()
-#define smp_mb__after_atomic()	barrier()
+#define __smp_mb__before_atomic()	barrier()
+#define __smp_mb__after_atomic()	barrier()
 
 #include <asm-generic/barrier.h>
 
-- 
MST

This defines __smp_xxx barriers for mips,
for use by virtualization.

smp_xxx barriers are removed as they are
defined correctly by asm-generic/barriers.h

Note: the only exception is smp_mb__before_llsc which is mips-specific.
We define both the __smp_mb__before_llsc variant (for use in
asm/barriers.h) and smp_mb__before_llsc (for use elsewhere on this
architecture).

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
---
 arch/mips/include/asm/barrier.h | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/arch/mips/include/asm/barrier.h b/arch/mips/include/asm/barrier.h
index 3eac4b9..d296633 100644
--- a/arch/mips/include/asm/barrier.h
+++ b/arch/mips/include/asm/barrier.h
@@ -85,20 +85,20 @@
 #define wmb()		fast_wmb()
 #define rmb()		fast_rmb()
 
-#if defined(CONFIG_WEAK_ORDERING) && defined(CONFIG_SMP)
+#if defined(CONFIG_WEAK_ORDERING)
 # ifdef CONFIG_CPU_CAVIUM_OCTEON
-#  define smp_mb()	__sync()
-#  define smp_rmb()	barrier()
-#  define smp_wmb()	__syncw()
+#  define __smp_mb()	__sync()
+#  define __smp_rmb()	barrier()
+#  define __smp_wmb()	__syncw()
 # else
-#  define smp_mb()	__asm__ __volatile__("sync" : :
:"memory")
-#  define smp_rmb()	__asm__ __volatile__("sync" : :
:"memory")
-#  define smp_wmb()	__asm__ __volatile__("sync" : :
:"memory")
+#  define __smp_mb()	__asm__ __volatile__("sync" : :
:"memory")
+#  define __smp_rmb()	__asm__ __volatile__("sync" : :
:"memory")
+#  define __smp_wmb()	__asm__ __volatile__("sync" : :
:"memory")
 # endif
 #else
-#define smp_mb()	barrier()
-#define smp_rmb()	barrier()
-#define smp_wmb()	barrier()
+#define __smp_mb()	barrier()
+#define __smp_rmb()	barrier()
+#define __smp_wmb()	barrier()
 #endif
 
 #if defined(CONFIG_WEAK_REORDERING_BEYOND_LLSC) && defined(CONFIG_SMP)
@@ -111,6 +111,7 @@
 
 #ifdef CONFIG_CPU_CAVIUM_OCTEON
 #define smp_mb__before_llsc() smp_wmb()
+#define __smp_mb__before_llsc() __smp_wmb()
 /* Cause previous writes to become visible on all CPUs as soon as possible */
 #define nudge_writes() __asm__ __volatile__(".set push\n\t"		\
 					    ".set arch=octeon\n\t"	\
@@ -118,11 +119,12 @@
 					    ".set pop" : : : "memory")
 #else
 #define smp_mb__before_llsc() smp_llsc_mb()
+#define __smp_mb__before_llsc() smp_llsc_mb()
 #define nudge_writes() mb()
 #endif
 
-#define smp_mb__before_atomic()	smp_mb__before_llsc()
-#define smp_mb__after_atomic()	smp_llsc_mb()
+#define __smp_mb__before_atomic()	__smp_mb__before_llsc()
+#define __smp_mb__after_atomic()	smp_llsc_mb()
 
 #include <asm-generic/barrier.h>
 
-- 
MST

This defines __smp_xxx barriers for s390,
for use by virtualization.

Some smp_xxx barriers are removed as they are
defined correctly by asm-generic/barriers.h

Note: smp_mb, smp_rmb and smp_wmb are defined as full barriers
unconditionally on this architecture.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
Acked-by: Martin Schwidefsky <schwidefsky at de.ibm.com>
---
 arch/s390/include/asm/barrier.h | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/arch/s390/include/asm/barrier.h b/arch/s390/include/asm/barrier.h
index c358c31..fbd25b2 100644
--- a/arch/s390/include/asm/barrier.h
+++ b/arch/s390/include/asm/barrier.h
@@ -26,18 +26,21 @@
 #define wmb()				barrier()
 #define dma_rmb()			mb()
 #define dma_wmb()			mb()
-#define smp_mb()			mb()
-#define smp_rmb()			rmb()
-#define smp_wmb()			wmb()
-
-#define smp_store_release(p, v)						\
+#define __smp_mb()			mb()
+#define __smp_rmb()			rmb()
+#define __smp_wmb()			wmb()
+#define smp_mb()			__smp_mb()
+#define smp_rmb()			__smp_rmb()
+#define smp_wmb()			__smp_wmb()
+
+#define __smp_store_release(p, v)					\
 do {									\
 	compiletime_assert_atomic_type(*p);				\
 	barrier();							\
 	WRITE_ONCE(*p, v);						\
 } while (0)
 
-#define smp_load_acquire(p)						\
+#define __smp_load_acquire(p)						\
 ({									\
 	typeof(*p) ___p1 = READ_ONCE(*p);				\
 	compiletime_assert_atomic_type(*p);				\
-- 
MST

sh variant of smp_store_mb() calls xchg() on !SMP which is stronger than
implied by both the name and the documentation.

define __smp_store_mb instead: code in asm-generic/barrier.h
will then define smp_store_mb correctly depending on
CONFIG_SMP.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
---
 arch/sh/include/asm/barrier.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/sh/include/asm/barrier.h b/arch/sh/include/asm/barrier.h
index bf91037..f887c64 100644
--- a/arch/sh/include/asm/barrier.h
+++ b/arch/sh/include/asm/barrier.h
@@ -32,7 +32,8 @@
 #define ctrl_barrier()	__asm__ __volatile__
("nop;nop;nop;nop;nop;nop;nop;nop")
 #endif
 
-#define smp_store_mb(var, value) do { (void)xchg(&var, value); } while (0)
+#define __smp_store_mb(var, value) do { (void)xchg(&var, value); } while
(0)
+#define smp_store_mb(var, value) __smp_store_mb(var, value)
 
 #include <asm-generic/barrier.h>
 
-- 
MST

This defines __smp_xxx barriers for sparc,
for use by virtualization.

smp_xxx barriers are removed as they are
defined correctly by asm-generic/barriers.h

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
Acked-by: David S. Miller <davem at davemloft.net>
---
 arch/sparc/include/asm/barrier_64.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/sparc/include/asm/barrier_64.h
b/arch/sparc/include/asm/barrier_64.h
index 26c3f72..c9f6ee6 100644
--- a/arch/sparc/include/asm/barrier_64.h
+++ b/arch/sparc/include/asm/barrier_64.h
@@ -37,14 +37,14 @@ do {	__asm__ __volatile__("ba,pt	%%xcc, 1f\n\t" \
 #define rmb()	__asm__ __volatile__("":::"memory")
 #define wmb()	__asm__ __volatile__("":::"memory")
 
-#define smp_store_release(p, v)						\
+#define __smp_store_release(p, v)						\
 do {									\
 	compiletime_assert_atomic_type(*p);				\
 	barrier();							\
 	WRITE_ONCE(*p, v);						\
 } while (0)
 
-#define smp_load_acquire(p)						\
+#define __smp_load_acquire(p)						\
 ({									\
 	typeof(*p) ___p1 = READ_ONCE(*p);				\
 	compiletime_assert_atomic_type(*p);				\
@@ -52,8 +52,8 @@ do {									\
 	___p1;								\
 })
 
-#define smp_mb__before_atomic()	barrier()
-#define smp_mb__after_atomic()	barrier()
+#define __smp_mb__before_atomic()	barrier()
+#define __smp_mb__after_atomic()	barrier()
 
 #include <asm-generic/barrier.h>
 
-- 
MST

This defines __smp_xxx barriers for tile,
for use by virtualization.

Some smp_xxx barriers are removed as they are
defined correctly by asm-generic/barriers.h

Note: for 32 bit, keep smp_mb__after_atomic around since it's faster
than the generic implementation.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
---
 arch/tile/include/asm/barrier.h | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/tile/include/asm/barrier.h b/arch/tile/include/asm/barrier.h
index 96a42ae..d552228 100644
--- a/arch/tile/include/asm/barrier.h
+++ b/arch/tile/include/asm/barrier.h
@@ -79,11 +79,12 @@ mb_incoherent(void)
  * But after the word is updated, the routine issues an "mf" before
returning,
  * and since it's a function call, we don't even need a compiler
barrier.
  */
-#define smp_mb__before_atomic()	smp_mb()
-#define smp_mb__after_atomic()	do { } while (0)
+#define __smp_mb__before_atomic()	__smp_mb()
+#define __smp_mb__after_atomic()	do { } while (0)
+#define smp_mb__after_atomic()	__smp_mb__after_atomic()
 #else /* 64 bit */
-#define smp_mb__before_atomic()	smp_mb()
-#define smp_mb__after_atomic()	smp_mb()
+#define __smp_mb__before_atomic()	__smp_mb()
+#define __smp_mb__after_atomic()	__smp_mb()
 #endif
 
 #include <asm-generic/barrier.h>
-- 
MST

This defines __smp_xxx barriers for xtensa,
for use by virtualization.

smp_xxx barriers are removed as they are
defined correctly by asm-generic/barriers.h

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
---
 arch/xtensa/include/asm/barrier.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/xtensa/include/asm/barrier.h
b/arch/xtensa/include/asm/barrier.h
index 5b88774..956596e 100644
--- a/arch/xtensa/include/asm/barrier.h
+++ b/arch/xtensa/include/asm/barrier.h
@@ -13,8 +13,8 @@
 #define rmb() barrier()
 #define wmb() mb()
 
-#define smp_mb__before_atomic()		barrier()
-#define smp_mb__after_atomic()		barrier()
+#define __smp_mb__before_atomic()		barrier()
+#define __smp_mb__after_atomic()		barrier()
 
 #include <asm-generic/barrier.h>
 
-- 
MST

This defines __smp_xxx barriers for x86,
for use by virtualization.

smp_xxx barriers are removed as they are
defined correctly by asm-generic/barriers.h

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Arnd Bergmann <arnd at arndb.de>
---
 arch/x86/include/asm/barrier.h | 31 ++++++++++++-------------------
 1 file changed, 12 insertions(+), 19 deletions(-)

diff --git a/arch/x86/include/asm/barrier.h b/arch/x86/include/asm/barrier.h
index cc4c2a7..a584e1c 100644
--- a/arch/x86/include/asm/barrier.h
+++ b/arch/x86/include/asm/barrier.h
@@ -31,17 +31,10 @@
 #endif
 #define dma_wmb()	barrier()
 
-#ifdef CONFIG_SMP
-#define smp_mb()	mb()
-#define smp_rmb()	dma_rmb()
-#define smp_wmb()	barrier()
-#define smp_store_mb(var, value) do { (void)xchg(&var, value); } while (0)
-#else /* !SMP */
-#define smp_mb()	barrier()
-#define smp_rmb()	barrier()
-#define smp_wmb()	barrier()
-#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); barrier(); }
while (0)
-#endif /* SMP */
+#define __smp_mb()	mb()
+#define __smp_rmb()	dma_rmb()
+#define __smp_wmb()	barrier()
+#define __smp_store_mb(var, value) do { (void)xchg(&var, value); } while
(0)
 
 #if defined(CONFIG_X86_PPRO_FENCE)
 
@@ -50,31 +43,31 @@
  * model and we should fall back to full barriers.
  */
 
-#define smp_store_release(p, v)						\
+#define __smp_store_release(p, v)					\
 do {									\
 	compiletime_assert_atomic_type(*p);				\
-	smp_mb();							\
+	__smp_mb();							\
 	WRITE_ONCE(*p, v);						\
 } while (0)
 
-#define smp_load_acquire(p)						\
+#define __smp_load_acquire(p)						\
 ({									\
 	typeof(*p) ___p1 = READ_ONCE(*p);				\
 	compiletime_assert_atomic_type(*p);				\
-	smp_mb();							\
+	__smp_mb();							\
 	___p1;								\
 })
 
 #else /* regular x86 TSO memory ordering */
 
-#define smp_store_release(p, v)						\
+#define __smp_store_release(p, v)					\
 do {									\
 	compiletime_assert_atomic_type(*p);				\
 	barrier();							\
 	WRITE_ONCE(*p, v);						\
 } while (0)
 
-#define smp_load_acquire(p)						\
+#define __smp_load_acquire(p)						\
 ({									\
 	typeof(*p) ___p1 = READ_ONCE(*p);				\
 	compiletime_assert_atomic_type(*p);				\
@@ -85,8 +78,8 @@ do {									\
 #endif
 
 /* Atomic operations are already serializing on x86 */
-#define smp_mb__before_atomic()	barrier()
-#define smp_mb__after_atomic()	barrier()
+#define __smp_mb__before_atomic()	barrier()
+#define __smp_mb__after_atomic()	barrier()
 
 #include <asm-generic/barrier.h>
 
-- 
MST

Guests running within virtual machines might be affected by SMP effects even if
the guest itself is compiled without SMP support.  This is an artifact of
interfacing with an SMP host while running an UP kernel.  Using mandatory
barriers for this use-case would be possible but is often suboptimal.

In particular, virtio uses a bunch of confusing ifdefs to work around
this, while xen just uses the mandatory barriers.

To better handle this case, low-level virt_mb() etc macros are made available.
These are implemented trivially using the low-level __smp_xxx macros,
the purpose of these wrappers is to annotate those specific cases.

These have the same effect as smp_mb() etc when SMP is enabled, but generate
identical code for SMP and non-SMP systems. For example, virtual machine guests
should use virt_mb() rather than smp_mb() when synchronizing against a
(possibly SMP) host.

Suggested-by: David Miller <davem at davemloft.net>
Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
 include/asm-generic/barrier.h     | 11 +++++++++++
 Documentation/memory-barriers.txt | 28 +++++++++++++++++++++++-----
 2 files changed, 34 insertions(+), 5 deletions(-)

diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
index 8752964..1cceca14 100644
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -196,5 +196,16 @@ do {									\
 
 #endif
 
+/* Barriers for virtual machine guests when talking to an SMP host */
+#define virt_mb() __smp_mb()
+#define virt_rmb() __smp_rmb()
+#define virt_wmb() __smp_wmb()
+#define virt_read_barrier_depends() __smp_read_barrier_depends()
+#define virt_store_mb(var, value) __smp_store_mb(var, value)
+#define virt_mb__before_atomic() __smp_mb__before_atomic()
+#define virt_mb__after_atomic()	__smp_mb__after_atomic()
+#define virt_store_release(p, v) __smp_store_release(p, v)
+#define virt_load_acquire(p) __smp_load_acquire(p)
+
 #endif /* !__ASSEMBLY__ */
 #endif /* __ASM_GENERIC_BARRIER_H */
diff --git a/Documentation/memory-barriers.txt
b/Documentation/memory-barriers.txt
index aef9487..8f4a93a 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -1655,17 +1655,18 @@ macro is a good place to start looking.
 SMP memory barriers are reduced to compiler barriers on uniprocessor compiled
 systems because it is assumed that a CPU will appear to be self-consistent,
 and will order overlapping accesses correctly with respect to itself.
+However, see the subsection on "Virtual Machine Guests" below.
 
 [!] Note that SMP memory barriers _must_ be used to control the ordering of
 references to shared memory on SMP systems, though the use of locking instead
 is sufficient.
 
 Mandatory barriers should not be used to control SMP effects, since mandatory
-barriers unnecessarily impose overhead on UP systems. They may, however, be
-used to control MMIO effects on accesses through relaxed memory I/O windows.
-These are required even on non-SMP systems as they affect the order in which
-memory operations appear to a device by prohibiting both the compiler and the
-CPU from reordering them.
+barriers impose unnecessary overhead on both SMP and UP systems. They may,
+however, be used to control MMIO effects on accesses through relaxed memory I/O
+windows.  These barriers are required even on non-SMP systems as they affect
+the order in which memory operations appear to a device by prohibiting both the
+compiler and the CPU from reordering them.
 
 
 There are some more advanced barrier functions:
@@ -2948,6 +2949,23 @@ The Alpha defines the Linux kernel's memory barrier
model.
 
 See the subsection on "Cache Coherency" above.
 
+VIRTUAL MACHINE GUESTS
+-------------------
+
+Guests running within virtual machines might be affected by SMP effects even if
+the guest itself is compiled without SMP support.  This is an artifact of
+interfacing with an SMP host while running an UP kernel.  Using mandatory
+barriers for this use-case would be possible but is often suboptimal.
+
+To handle this case optimally, low-level virt_mb() etc macros are available.
+These have the same effect as smp_mb() etc when SMP is enabled, but generate
+identical code for SMP and non-SMP systems. For example, virtual machine guests
+should use virt_mb() rather than smp_mb() when synchronizing against a
+(possibly SMP) host.
+
+These are equivalent to smp_mb() etc counterparts in all other respects,
+in particular, they do not control MMIO effects: to control
+MMIO effects, use mandatory barriers.
 
 =========== EXAMPLE USES
-- 
MST

This reverts commit 9e1a27ea42691429e31f158cce6fc61bc79bb2e9.

While that commit optimizes !CONFIG_SMP, it mixes
up DMA and SMP concepts, making the code hard
to figure out.

A better way to optimize this is with the new __smp_XXX
barriers.

As a first step, go back to full rmb/wmb barriers
for !SMP.
We switch to __smp_XXX barriers in the next patch.

Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Alexander Duyck <alexander.duyck at gmail.com>
Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
 include/linux/virtio_ring.h | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index 8e50888..67e06fe 100644
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h
@@ -21,20 +21,19 @@
  * actually quite cheap.
  */
 
+#ifdef CONFIG_SMP
 static inline void virtio_mb(bool weak_barriers)
 {
-#ifdef CONFIG_SMP
 	if (weak_barriers)
 		smp_mb();
 	else
-#endif
 		mb();
 }
 
 static inline void virtio_rmb(bool weak_barriers)
 {
 	if (weak_barriers)
-		dma_rmb();
+		smp_rmb();
 	else
 		rmb();
 }
@@ -42,10 +41,26 @@ static inline void virtio_rmb(bool weak_barriers)
 static inline void virtio_wmb(bool weak_barriers)
 {
 	if (weak_barriers)
-		dma_wmb();
+		smp_wmb();
 	else
 		wmb();
 }
+#else
+static inline void virtio_mb(bool weak_barriers)
+{
+	mb();
+}
+
+static inline void virtio_rmb(bool weak_barriers)
+{
+	rmb();
+}
+
+static inline void virtio_wmb(bool weak_barriers)
+{
+	wmb();
+}
+#endif
 
 struct virtio_device;
 struct virtqueue;
-- 
MST

virtio ring uses smp_wmb on SMP and wmb on !SMP,
the reason for the later being that it might be
talking to another kernel on the same SMP machine.

This is exactly what virt_xxx barriers do,
so switch to these instead of homegrown ifdef hacks.

Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Alexander Duyck <alexander.duyck at gmail.com>
Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
 include/linux/virtio_ring.h | 25 ++++---------------------
 1 file changed, 4 insertions(+), 21 deletions(-)

diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index 67e06fe..f3fa55b 100644
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h
@@ -12,7 +12,7 @@
  * anyone care?
  *
  * For virtio_pci on SMP, we don't need to order with respect to MMIO
- * accesses through relaxed memory I/O windows, so smp_mb() et al are
+ * accesses through relaxed memory I/O windows, so virt_mb() et al are
  * sufficient.
  *
  * For using virtio to talk to real devices (eg. other heterogeneous
@@ -21,11 +21,10 @@
  * actually quite cheap.
  */
 
-#ifdef CONFIG_SMP
 static inline void virtio_mb(bool weak_barriers)
 {
 	if (weak_barriers)
-		smp_mb();
+		virt_mb();
 	else
 		mb();
 }
@@ -33,7 +32,7 @@ static inline void virtio_mb(bool weak_barriers)
 static inline void virtio_rmb(bool weak_barriers)
 {
 	if (weak_barriers)
-		smp_rmb();
+		virt_rmb();
 	else
 		rmb();
 }
@@ -41,26 +40,10 @@ static inline void virtio_rmb(bool weak_barriers)
 static inline void virtio_wmb(bool weak_barriers)
 {
 	if (weak_barriers)
-		smp_wmb();
+		virt_wmb();
 	else
 		wmb();
 }
-#else
-static inline void virtio_mb(bool weak_barriers)
-{
-	mb();
-}
-
-static inline void virtio_rmb(bool weak_barriers)
-{
-	rmb();
-}
-
-static inline void virtio_wmb(bool weak_barriers)
-{
-	wmb();
-}
-#endif
 
 struct virtio_device;
 struct virtqueue;
-- 
MST

This completes the xchg implementation for sh architecture.  Note: The
llsc variant is tricky since this only supports 4 byte atomics, the
existing implementation of 1 byte xchg is wrong: we need to do a 4 byte
cmpxchg and retry if any bytes changed meanwhile.

Write this in C for clarity.

Suggested-by: Rich Felker <dalias at libc.org>
Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
 arch/sh/include/asm/cmpxchg-grb.h  | 22 +++++++++++++++
 arch/sh/include/asm/cmpxchg-irq.h  | 11 ++++++++
 arch/sh/include/asm/cmpxchg-llsc.h | 58 +++++++++++++++++++++++---------------
 arch/sh/include/asm/cmpxchg.h      |  3 ++
 4 files changed, 72 insertions(+), 22 deletions(-)

diff --git a/arch/sh/include/asm/cmpxchg-grb.h
b/arch/sh/include/asm/cmpxchg-grb.h
index f848dec..2ed557b 100644
--- a/arch/sh/include/asm/cmpxchg-grb.h
+++ b/arch/sh/include/asm/cmpxchg-grb.h
@@ -23,6 +23,28 @@ static inline unsigned long xchg_u32(volatile u32 *m,
unsigned long val)
 	return retval;
 }
 
+static inline unsigned long xchg_u16(volatile u16 *m, unsigned long val)
+{
+	unsigned long retval;
+
+	__asm__ __volatile__ (
+		"   .align  2             \n\t"
+		"   mova    1f,   r0      \n\t" /* r0 = end point */
+		"   mov    r15,   r1      \n\t" /* r1 = saved sp */
+		"   mov    #-6,   r15     \n\t" /* LOGIN */
+		"   mov.w  @%1,   %0      \n\t" /* load  old value */
+		"   extu.w  %0,   %0      \n\t" /* extend as unsigned */
+		"   mov.w   %2,   @%1     \n\t" /* store new value */
+		"1: mov     r1,   r15     \n\t" /* LOGOUT */
+		: "=&r" (retval),
+		  "+r"  (m),
+		  "+r"  (val)		/* inhibit r15 overloading */
+		:
+		: "memory" , "r0", "r1");
+
+	return retval;
+}
+
 static inline unsigned long xchg_u8(volatile u8 *m, unsigned long val)
 {
 	unsigned long retval;
diff --git a/arch/sh/include/asm/cmpxchg-irq.h
b/arch/sh/include/asm/cmpxchg-irq.h
index bd11f63..f888772 100644
--- a/arch/sh/include/asm/cmpxchg-irq.h
+++ b/arch/sh/include/asm/cmpxchg-irq.h
@@ -14,6 +14,17 @@ static inline unsigned long xchg_u32(volatile u32 *m,
unsigned long val)
 	return retval;
 }
 
+static inline unsigned long xchg_u16(volatile u16 *m, unsigned long val)
+{
+	unsigned long flags, retval;
+
+	local_irq_save(flags);
+	retval = *m;
+	*m = val;
+	local_irq_restore(flags);
+	return retval;
+}
+
 static inline unsigned long xchg_u8(volatile u8 *m, unsigned long val)
 {
 	unsigned long flags, retval;
diff --git a/arch/sh/include/asm/cmpxchg-llsc.h
b/arch/sh/include/asm/cmpxchg-llsc.h
index 4713666..e754794 100644
--- a/arch/sh/include/asm/cmpxchg-llsc.h
+++ b/arch/sh/include/asm/cmpxchg-llsc.h
@@ -1,6 +1,9 @@
 #ifndef __ASM_SH_CMPXCHG_LLSC_H
 #define __ASM_SH_CMPXCHG_LLSC_H
 
+#include <linux/bitops.h>
+#include <asm/byteorder.h>
+
 static inline unsigned long xchg_u32(volatile u32 *m, unsigned long val)
 {
 	unsigned long retval;
@@ -22,29 +25,8 @@ static inline unsigned long xchg_u32(volatile u32 *m,
unsigned long val)
 	return retval;
 }
 
-static inline unsigned long xchg_u8(volatile u8 *m, unsigned long val)
-{
-	unsigned long retval;
-	unsigned long tmp;
-
-	__asm__ __volatile__ (
-		"1:					\n\t"
-		"movli.l	@%2, %0	! xchg_u8	\n\t"
-		"mov		%0, %1			\n\t"
-		"mov		%3, %0			\n\t"
-		"movco.l	%0, @%2			\n\t"
-		"bf		1b			\n\t"
-		"synco					\n\t"
-		: "=&z"(tmp), "=&r" (retval)
-		: "r" (m), "r" (val & 0xff)
-		: "t", "memory"
-	);
-
-	return retval;
-}
-
 static inline unsigned long
-__cmpxchg_u32(volatile int *m, unsigned long old, unsigned long new)
+__cmpxchg_u32(volatile u32 *m, unsigned long old, unsigned long new)
 {
 	unsigned long retval;
 	unsigned long tmp;
@@ -68,4 +50,36 @@ __cmpxchg_u32(volatile int *m, unsigned long old, unsigned
long new)
 	return retval;
 }
 
+static inline u32 __xchg_cmpxchg(volatile void *ptr, u32 x, int size)
+{
+	int off = (unsigned long)ptr % sizeof(u32);
+	volatile u32 *p = ptr - off;
+#ifdef __BIG_ENDIAN
+	int bitoff = (sizeof(u32) - 1 - off) * BITS_PER_BYTE;
+#else
+	int bitoff = off * BITS_PER_BYTE;
+#endif
+	u32 bitmask = ((0x1 << size * BITS_PER_BYTE) - 1) << bitoff;
+	u32 oldv, newv;
+	u32 ret;
+
+	do {
+		oldv = READ_ONCE(*p);
+		ret = (oldv & bitmask) >> bitoff;
+		newv = (oldv & ~bitmask) | (x << bitoff);
+	} while (__cmpxchg_u32(p, oldv, newv) != oldv);
+
+	return ret;
+}
+
+static inline unsigned long xchg_u16(volatile u16 *m, unsigned long val)
+{
+	return __xchg_cmpxchg(m, val, sizeof *m);
+}
+
+static inline unsigned long xchg_u8(volatile u8 *m, unsigned long val)
+{
+	return __xchg_cmpxchg(m, val, sizeof *m);
+}
+
 #endif /* __ASM_SH_CMPXCHG_LLSC_H */
diff --git a/arch/sh/include/asm/cmpxchg.h b/arch/sh/include/asm/cmpxchg.h
index 85c97b18..5225916 100644
--- a/arch/sh/include/asm/cmpxchg.h
+++ b/arch/sh/include/asm/cmpxchg.h
@@ -27,6 +27,9 @@ extern void __xchg_called_with_bad_pointer(void);
 	case 4:						\
 		__xchg__res = xchg_u32(__xchg_ptr, x);	\
 		break;					\
+	case 2:						\
+		__xchg__res = xchg_u16(__xchg_ptr, x);	\
+		break;					\
 	case 1:						\
 		__xchg__res = xchg_u8(__xchg_ptr, x);	\
 		break;					\
-- 
MST

Looks like future sh variants will support a 4-byte cas which will be
used to implement 1 and 2 byte xchg.

This is exactly what we do for llsc now, move the portable part of the
code into a separate header so it's easy to reuse.

Suggested-by:  Rich Felker <dalias at libc.org>
Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
 arch/sh/include/asm/cmpxchg-llsc.h | 35 +-------------------------
 arch/sh/include/asm/cmpxchg-xchg.h | 51 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 52 insertions(+), 34 deletions(-)
 create mode 100644 arch/sh/include/asm/cmpxchg-xchg.h

diff --git a/arch/sh/include/asm/cmpxchg-llsc.h
b/arch/sh/include/asm/cmpxchg-llsc.h
index e754794..fcfd322 100644
--- a/arch/sh/include/asm/cmpxchg-llsc.h
+++ b/arch/sh/include/asm/cmpxchg-llsc.h
@@ -1,9 +1,6 @@
 #ifndef __ASM_SH_CMPXCHG_LLSC_H
 #define __ASM_SH_CMPXCHG_LLSC_H
 
-#include <linux/bitops.h>
-#include <asm/byteorder.h>
-
 static inline unsigned long xchg_u32(volatile u32 *m, unsigned long val)
 {
 	unsigned long retval;
@@ -50,36 +47,6 @@ __cmpxchg_u32(volatile u32 *m, unsigned long old, unsigned
long new)
 	return retval;
 }
 
-static inline u32 __xchg_cmpxchg(volatile void *ptr, u32 x, int size)
-{
-	int off = (unsigned long)ptr % sizeof(u32);
-	volatile u32 *p = ptr - off;
-#ifdef __BIG_ENDIAN
-	int bitoff = (sizeof(u32) - 1 - off) * BITS_PER_BYTE;
-#else
-	int bitoff = off * BITS_PER_BYTE;
-#endif
-	u32 bitmask = ((0x1 << size * BITS_PER_BYTE) - 1) << bitoff;
-	u32 oldv, newv;
-	u32 ret;
-
-	do {
-		oldv = READ_ONCE(*p);
-		ret = (oldv & bitmask) >> bitoff;
-		newv = (oldv & ~bitmask) | (x << bitoff);
-	} while (__cmpxchg_u32(p, oldv, newv) != oldv);
-
-	return ret;
-}
-
-static inline unsigned long xchg_u16(volatile u16 *m, unsigned long val)
-{
-	return __xchg_cmpxchg(m, val, sizeof *m);
-}
-
-static inline unsigned long xchg_u8(volatile u8 *m, unsigned long val)
-{
-	return __xchg_cmpxchg(m, val, sizeof *m);
-}
+#include <asm/cmpxchg-xchg.h>
 
 #endif /* __ASM_SH_CMPXCHG_LLSC_H */
diff --git a/arch/sh/include/asm/cmpxchg-xchg.h
b/arch/sh/include/asm/cmpxchg-xchg.h
new file mode 100644
index 0000000..7219719
--- /dev/null
+++ b/arch/sh/include/asm/cmpxchg-xchg.h
@@ -0,0 +1,51 @@
+#ifndef __ASM_SH_CMPXCHG_XCHG_H
+#define __ASM_SH_CMPXCHG_XCHG_H
+
+/*
+ * Copyright (C) 2016 Red Hat, Inc.
+ * Author: Michael S. Tsirkin <mst at redhat.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See the
+ * file "COPYING" in the main directory of this archive for more
details.
+ */
+#include <linux/bitops.h>
+#include <asm/byteorder.h>
+
+/*
+ * Portable implementations of 1 and 2 byte xchg using a 4 byte cmpxchg.
+ * Note: this header isn't self-contained: before including it,
__cmpxchg_u32
+ * must be defined first.
+ */
+static inline u32 __xchg_cmpxchg(volatile void *ptr, u32 x, int size)
+{
+	int off = (unsigned long)ptr % sizeof(u32);
+	volatile u32 *p = ptr - off;
+#ifdef __BIG_ENDIAN
+	int bitoff = (sizeof(u32) - 1 - off) * BITS_PER_BYTE;
+#else
+	int bitoff = off * BITS_PER_BYTE;
+#endif
+	u32 bitmask = ((0x1 << size * BITS_PER_BYTE) - 1) << bitoff;
+	u32 oldv, newv;
+	u32 ret;
+
+	do {
+		oldv = READ_ONCE(*p);
+		ret = (oldv & bitmask) >> bitoff;
+		newv = (oldv & ~bitmask) | (x << bitoff);
+	} while (__cmpxchg_u32(p, oldv, newv) != oldv);
+
+	return ret;
+}
+
+static inline unsigned long xchg_u16(volatile u16 *m, unsigned long val)
+{
+	return __xchg_cmpxchg(m, val, sizeof *m);
+}
+
+static inline unsigned long xchg_u8(volatile u8 *m, unsigned long val)
+{
+	return __xchg_cmpxchg(m, val, sizeof *m);
+}
+
+#endif /* __ASM_SH_CMPXCHG_XCHG_H */
-- 
MST

We need a full barrier after writing out event index, using
virt_store_mb there seems better than open-coding.  As usual, we need a
wrapper to account for strong barriers.

It's tempting to use this in vhost as well, for that, we'll
need a variant of smp_store_mb that works on __user pointers.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
 include/linux/virtio_ring.h  | 11 +++++++++++
 drivers/virtio/virtio_ring.c | 15 +++++++++------
 2 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index f3fa55b..a156e2b 100644
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h
@@ -45,6 +45,17 @@ static inline void virtio_wmb(bool weak_barriers)
 		wmb();
 }
 
+static inline void virtio_store_mb(bool weak_barriers,
+				   __virtio16 *p, __virtio16 v)
+{
+	if (weak_barriers) {
+		virt_store_mb(*p, v);
+	} else {
+		WRITE_ONCE(*p, v);
+		mb();
+	}
+}
+
 struct virtio_device;
 struct virtqueue;
 
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index ee663c4..e12e385 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -517,10 +517,10 @@ void *virtqueue_get_buf(struct virtqueue *_vq, unsigned
int *len)
 	/* If we expect an interrupt for the next entry, tell host
 	 * by writing event index and flush out the write before
 	 * the read in the next get_buf call. */
-	if (!(vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT)) {
-		vring_used_event(&vq->vring) = cpu_to_virtio16(_vq->vdev,
vq->last_used_idx);
-		virtio_mb(vq->weak_barriers);
-	}
+	if (!(vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT))
+		virtio_store_mb(vq->weak_barriers,
+				&vring_used_event(&vq->vring),
+				cpu_to_virtio16(_vq->vdev, vq->last_used_idx));
 
 #ifdef DEBUG
 	vq->last_add_time_valid = false;
@@ -653,8 +653,11 @@ bool virtqueue_enable_cb_delayed(struct virtqueue *_vq)
 	}
 	/* TODO: tune this threshold */
 	bufs = (u16)(vq->avail_idx_shadow - vq->last_used_idx) * 3 / 4;
-	vring_used_event(&vq->vring) = cpu_to_virtio16(_vq->vdev,
vq->last_used_idx + bufs);
-	virtio_mb(vq->weak_barriers);
+
+	virtio_store_mb(vq->weak_barriers,
+			&vring_used_event(&vq->vring),
+			cpu_to_virtio16(_vq->vdev, vq->last_used_idx + bufs));
+
 	if (unlikely((u16)(virtio16_to_cpu(_vq->vdev, vq->vring.used->idx) -
vq->last_used_idx) > bufs)) {
 		END_USE(vq);
 		return false;
-- 
MST

SMP-only barriers were missing in checkpatch.pl

Refactor code slightly to make adding more variants easier.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
 scripts/checkpatch.pl | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 2b3c228..97b8b62 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -5116,7 +5116,25 @@ sub process {
 			}
 		}
 # check for memory barriers without a comment.
-		if ($line =~
/\b(mb|rmb|wmb|read_barrier_depends|smp_mb|smp_rmb|smp_wmb|smp_read_barrier_depends)\(/)
{
+
+		my $barriers = qr{
+			mb|
+			rmb|
+			wmb|
+			read_barrier_depends
+		}x;
+		my $smp_barriers = qr{
+			store_release|
+			load_acquire|
+			store_mb|
+			($barriers)
+		}x;
+		my $all_barriers = qr{
+			$barriers|
+			smp_($smp_barriers)
+		}x;
+
+		if ($line =~ /\b($all_barriers)\s*\(/) {
 			if (!ctx_has_comment($first_line, $linenr)) {
 				WARN("MEMORY_BARRIER",
 				     "memory barrier without comment\n" . $herecurr);
-- 
MST

Introduction of __smp barriers cleans up a bunch of duplicate code, but
it gives people an additional handle onto a "new" set of barriers -
just
because they're prefixed with __* unfortunately doesn't stop anyone from
using it (as happened with other arch stuff before.)

Add a checkpatch test so it will trigger a warning.

Reported-by: Russell King <linux at arm.linux.org.uk>
Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
 scripts/checkpatch.pl | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 97b8b62..a96adcb 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -5141,6 +5141,16 @@ sub process {
 			}
 		}
 
+		my $underscore_smp_barriers = qr{__smp_($smp_barriers)}x;
+
+		if ($realfile !~ m@^include/asm-generic/@ &&
+		    $realfile !~ m@/barrier\.h$@ &&
+		    $line =~ m/\b($underscore_smp_barriers)\s*\(/ &&
+		    $line !~ m/^.\s*\#\s*define\s+($underscore_smp_barriers)\s*\(/) {
+			WARN("MEMORY_BARRIER",
+			     "__smp memory barriers shouldn't be used outside barrier.h and
asm-generic\n" . $herecurr);
+		}
+
 # check for waitqueue_active without a comment.
 		if ($line =~ /\bwaitqueue_active\s*\(/) {
 			if (!ctx_has_comment($first_line, $linenr)) {
-- 
MST

Add virt_ barriers to list of barriers to check for
presence of a comment.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
 scripts/checkpatch.pl | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index a96adcb..5ca272b 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -5131,7 +5131,8 @@ sub process {
 		}x;
 		my $all_barriers = qr{
 			$barriers|
-			smp_($smp_barriers)
+			smp_($smp_barriers)|
+			virt_($smp_barriers)
 		}x;
 
 		if ($line =~ /\b($all_barriers)\s*\(/) {
-- 
MST

drivers/xen/xenbus/xenbus_comms.c uses
full memory barriers to communicate with the other side.

For guests compiled with CONFIG_SMP, smp_wmb and smp_mb
would be sufficient, so mb() and wmb() here are only needed if
a non-SMP guest runs on an SMP host.

Switch to virt_xxx barriers which serve this exact purpose.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: David Vrabel <david.vrabel at citrix.com>
---
 drivers/xen/xenbus/xenbus_comms.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/xen/xenbus/xenbus_comms.c
b/drivers/xen/xenbus/xenbus_comms.c
index fdb0f33..ecdecce 100644
--- a/drivers/xen/xenbus/xenbus_comms.c
+++ b/drivers/xen/xenbus/xenbus_comms.c
@@ -123,14 +123,14 @@ int xb_write(const void *data, unsigned len)
 			avail = len;
 
 		/* Must write data /after/ reading the consumer index. */
-		mb();
+		virt_mb();
 
 		memcpy(dst, data, avail);
 		data += avail;
 		len -= avail;
 
 		/* Other side must not see new producer until data is there. */
-		wmb();
+		virt_wmb();
 		intf->req_prod += avail;
 
 		/* Implies mb(): other side will see the updated producer. */
@@ -180,14 +180,14 @@ int xb_read(void *data, unsigned len)
 			avail = len;
 
 		/* Must read data /after/ reading the producer index. */
-		rmb();
+		virt_rmb();
 
 		memcpy(data, src, avail);
 		data += avail;
 		len -= avail;
 
 		/* Other side must not see free space until we've copied out */
-		mb();
+		virt_mb();
 		intf->rsp_cons += avail;
 
 		pr_debug("Finished read of %i bytes (%i to go)\n", avail, len);
-- 
MST

include/xen/interface/io/ring.h uses
full memory barriers to communicate with the other side.

For guests compiled with CONFIG_SMP, smp_wmb and smp_mb
would be sufficient, so mb() and wmb() here are only needed if
a non-SMP guest runs on an SMP host.

Switch to virt_xxx barriers which serve this exact purpose.

Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: David Vrabel <david.vrabel at citrix.com>
---
 include/xen/interface/io/ring.h | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/include/xen/interface/io/ring.h b/include/xen/interface/io/ring.h
index 7dc685b..21f4fbd 100644
--- a/include/xen/interface/io/ring.h
+++ b/include/xen/interface/io/ring.h
@@ -208,12 +208,12 @@ struct __name##_back_ring {						\
 
 
 #define RING_PUSH_REQUESTS(_r) do {					\
-    wmb(); /* back sees requests /before/ updated producer index */	\
+    virt_wmb(); /* back sees requests /before/ updated producer index */	\
     (_r)->sring->req_prod = (_r)->req_prod_pvt;				\
 } while (0)
 
 #define RING_PUSH_RESPONSES(_r) do {					\
-    wmb(); /* front sees responses /before/ updated producer index */	\
+    virt_wmb(); /* front sees responses /before/ updated producer index */	\
     (_r)->sring->rsp_prod = (_r)->rsp_prod_pvt;				\
 } while (0)
 
@@ -250,9 +250,9 @@ struct __name##_back_ring {						\
 #define RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(_r, _notify) do {		\
     RING_IDX __old = (_r)->sring->req_prod;				\
     RING_IDX __new = (_r)->req_prod_pvt;				\
-    wmb(); /* back sees requests /before/ updated producer index */	\
+    virt_wmb(); /* back sees requests /before/ updated producer index */	\
     (_r)->sring->req_prod = __new;					\
-    mb(); /* back sees new requests /before/ we check req_event */	\
+    virt_mb(); /* back sees new requests /before/ we check req_event */	\
     (_notify) = ((RING_IDX)(__new - (_r)->sring->req_event) <		\
 		 (RING_IDX)(__new - __old));				\
 } while (0)
@@ -260,9 +260,9 @@ struct __name##_back_ring {						\
 #define RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(_r, _notify) do {		\
     RING_IDX __old = (_r)->sring->rsp_prod;				\
     RING_IDX __new = (_r)->rsp_prod_pvt;				\
-    wmb(); /* front sees responses /before/ updated producer index */	\
+    virt_wmb(); /* front sees responses /before/ updated producer index */	\
     (_r)->sring->rsp_prod = __new;					\
-    mb(); /* front sees new responses /before/ we check rsp_event */	\
+    virt_mb(); /* front sees new responses /before/ we check rsp_event */	\
     (_notify) = ((RING_IDX)(__new - (_r)->sring->rsp_event) <		\
 		 (RING_IDX)(__new - __old));				\
 } while (0)
@@ -271,7 +271,7 @@ struct __name##_back_ring {						\
     (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r);			\
     if (_work_to_do) break;						\
     (_r)->sring->req_event = (_r)->req_cons + 1;			\
-    mb();								\
+    virt_mb();								\
     (_work_to_do) = RING_HAS_UNCONSUMED_REQUESTS(_r);			\
 } while (0)
 
@@ -279,7 +279,7 @@ struct __name##_back_ring {						\
     (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r);			\
     if (_work_to_do) break;						\
     (_r)->sring->rsp_event = (_r)->rsp_cons + 1;			\
-    mb();								\
+    virt_mb();								\
     (_work_to_do) = RING_HAS_UNCONSUMED_RESPONSES(_r);			\
 } while (0)
 
-- 
MST

drivers/xen/events/events_fifo.c uses rmb() to communicate with the
other side.

For guests compiled with CONFIG_SMP, smp_rmb would be sufficient, so
rmb() here is only needed if a non-SMP guest runs on an SMP host.

Switch to the virt_rmb barrier which serves this exact purpose.

Pull in asm/barrier.h here to make sure the file is self-contained.

Suggested-by: David Vrabel <david.vrabel at citrix.com>
Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
 drivers/xen/events/events_fifo.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/xen/events/events_fifo.c b/drivers/xen/events/events_fifo.c
index 96a1b8d..eff2b88 100644
--- a/drivers/xen/events/events_fifo.c
+++ b/drivers/xen/events/events_fifo.c
@@ -41,6 +41,7 @@
 #include <linux/percpu.h>
 #include <linux/cpu.h>
 
+#include <asm/barrier.h>
 #include <asm/sync_bitops.h>
 #include <asm/xen/hypercall.h>
 #include <asm/xen/hypervisor.h>
@@ -296,7 +297,7 @@ static void consume_one_event(unsigned cpu,
 	 * control block.
 	 */
 	if (head == 0) {
-		rmb(); /* Ensure word is up-to-date before reading head. */
+		virt_rmb(); /* Ensure word is up-to-date before reading head. */
 		head = control_block->head[priority];
 	}
 
-- 
MST

The s390 kernel is SMP to 99.99%, we just didn't bother with a
non-smp variant for the memory-barriers. If the generic header
is used we'd get the non-smp version for free. It will save a
small amount of text space for CONFIG_SMP=n.

Suggested-by: Martin Schwidefsky <schwidefsky at de.ibm.com>
Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
 arch/s390/include/asm/barrier.h | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/arch/s390/include/asm/barrier.h b/arch/s390/include/asm/barrier.h
index fbd25b2..4d26fa4 100644
--- a/arch/s390/include/asm/barrier.h
+++ b/arch/s390/include/asm/barrier.h
@@ -29,9 +29,6 @@
 #define __smp_mb()			mb()
 #define __smp_rmb()			rmb()
 #define __smp_wmb()			wmb()
-#define smp_mb()			__smp_mb()
-#define smp_rmb()			__smp_rmb()
-#define smp_wmb()			__smp_wmb()
 
 #define __smp_store_release(p, v)					\
 do {									\
-- 
MST

As per: lkml.kernel.org/r/20150921112252.3c2937e1 at mschwide
atomics imply a barrier on s390, so s390 should change
smp_mb__before_atomic and smp_mb__after_atomic to barrier() instead of
smp_mb() and hence should not use the generic versions.

Suggested-by: Peter Zijlstra <peterz at infradead.org>
Suggested-by: Martin Schwidefsky <schwidefsky at de.ibm.com>
Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
---
 arch/s390/include/asm/barrier.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/s390/include/asm/barrier.h b/arch/s390/include/asm/barrier.h
index 4d26fa4..5c8db3c 100644
--- a/arch/s390/include/asm/barrier.h
+++ b/arch/s390/include/asm/barrier.h
@@ -45,6 +45,9 @@ do {									\
 	___p1;								\
 })
 
+#define __smp_mb__before_atomic()	barrier()
+#define __smp_mb__after_atomic()	barrier()
+
 #include <asm-generic/barrier.h>
 
 #endif /* __ASM_BARRIER_H */
-- 
MST

On 10/01/16 14:21, Michael S. Tsirkin wrote:
> drivers/xen/events/events_fifo.c uses rmb() to communicate with the
> other side.
> 
> For guests compiled with CONFIG_SMP, smp_rmb would be sufficient, so
> rmb() here is only needed if a non-SMP guest runs on an SMP host.
> 
> Switch to the virt_rmb barrier which serves this exact purpose.
> 
> Pull in asm/barrier.h here to make sure the file is self-contained.
> 
> Suggested-by: David Vrabel <david.vrabel at citrix.com>
> Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: David Vrabel <david.vrabel at citrix.com>

David

On 01/10/2016 06:18 AM, Michael S. Tsirkin wrote:
> On mips dma_rmb, dma_wmb, smp_store_mb, read_barrier_depends,
> smp_read_barrier_depends, smp_store_release and smp_load_acquire  match
> the asm-generic variants exactly. Drop the local definitions and pull in
> asm-generic/barrier.h instead.
>
This statement doesn't fit MIPS barriers variations. Moreover, there is 
a reason to extend that even more specific, at least for 
smp_store_release and smp_load_acquire, look into

     http://patchwork.linux-mips.org/patch/10506/

- Leonid.

On Sun, Jan 10, 2016 at 04:16:22PM +0200, Michael S. Tsirkin
wrote:
> I parked this in vhost tree for now, though the inclusion of patch 1 from
tip
> creates a merge conflict - but one that is trivial to resolve.
> 
> So I intend to just merge it all through my tree, including the
> duplicate patch, and assume conflict will be resolved.
> 
> I would really appreciate some feedback on arch bits (especially the x86
bits),
> and acks for merging this through the vhost tree.
Thanks for doing this, looks good to me.

Acked-by: Peter Zijlstra (Intel) <peterz at infradead.org>

On Sun, 10 Jan 2016, Michael S. Tsirkin wrote:
> As on most architectures, on x86 read_barrier_depends and
> smp_read_barrier_depends are empty.  Drop the local definitions and pull
> the generic ones from asm-generic/barrier.h instead: they are identical.
> 
> This is in preparation to refactoring this code area.
> 
> Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
> Acked-by: Arnd Bergmann <arnd at arndb.de>
Reviewed-by: Thomas Gleixner <tglx at linutronix.de>

On Sun, 10 Jan 2016, Michael S. Tsirkin wrote:
> This defines __smp_xxx barriers for x86,
> for use by virtualization.
> 
> smp_xxx barriers are removed as they are
> defined correctly by asm-generic/barriers.h
> 
> Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
> Acked-by: Arnd Bergmann <arnd at arndb.de>
Reviewed-by: Thomas Gleixner <tglx at linutronix.de>

On Sun, Jan 10, 2016 at 04:16:32PM +0200, Michael S. Tsirkin
wrote:
> From: Davidlohr Bueso <dave at stgolabs.net>
> 
> With commit b92b8b35a2e ("locking/arch: Rename set_mb() to
smp_store_mb()")
> it was made clear that the context of this call (and thus set_mb)
> is strictly for CPU ordering, as opposed to IO. As such all archs
> should use the smp variant of mb(), respecting the semantics and
> saving a mandatory barrier on UP.
> 
> Signed-off-by: Davidlohr Bueso <dbueso at suse.de>
> Signed-off-by: Peter Zijlstra (Intel) <peterz at infradead.org>
> Cc: <linux-arch at vger.kernel.org>
> Cc: Andrew Morton <akpm at linux-foundation.org>
> Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
> Cc: Heiko Carstens <heiko.carstens at de.ibm.com>
> Cc: Linus Torvalds <torvalds at linux-foundation.org>
> Cc: Paul E. McKenney <paulmck at linux.vnet.ibm.com>
> Cc: Peter Zijlstra <peterz at infradead.org>
> Cc: Thomas Gleixner <tglx at linutronix.de>
> Cc: Tony Luck <tony.luck at intel.com>
> Cc: dave at stgolabs.net
> Link: http://lkml.kernel.org/r/1445975631-17047-3-git-send-email-dave at
stgolabs.net
> Signed-off-by: Ingo Molnar <mingo at kernel.org>
Aside from a need for s/lcoking/locking/ in the subject line:

Reviewed-by: Paul E. McKenney <paulmck at linux.vnet.ibm.com>
> ---
>  arch/ia64/include/asm/barrier.h    | 2 +-
>  arch/powerpc/include/asm/barrier.h | 2 +-
>  arch/s390/include/asm/barrier.h    | 2 +-
>  include/asm-generic/barrier.h      | 2 +-
>  4 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/ia64/include/asm/barrier.h
b/arch/ia64/include/asm/barrier.h
> index df896a1..209c4b8 100644
> --- a/arch/ia64/include/asm/barrier.h
> +++ b/arch/ia64/include/asm/barrier.h
> @@ -77,7 +77,7 @@ do {									\
>  	___p1;								\
>  })
> 
> -#define smp_store_mb(var, value)	do { WRITE_ONCE(var, value); mb(); }
while (0)
> +#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); }
while (0)
> 
>  /*
>   * The group barrier in front of the rsm & ssm are necessary to ensure
> diff --git a/arch/powerpc/include/asm/barrier.h
b/arch/powerpc/include/asm/barrier.h
> index 0eca6ef..a7af5fb 100644
> --- a/arch/powerpc/include/asm/barrier.h
> +++ b/arch/powerpc/include/asm/barrier.h
> @@ -34,7 +34,7 @@
>  #define rmb()  __asm__ __volatile__ ("sync" : : :
"memory")
>  #define wmb()  __asm__ __volatile__ ("sync" : : :
"memory")
> 
> -#define smp_store_mb(var, value)	do { WRITE_ONCE(var, value); mb(); }
while (0)
> +#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); }
while (0)
> 
>  #ifdef __SUBARCH_HAS_LWSYNC
>  #    define SMPWMB      LWSYNC
> diff --git a/arch/s390/include/asm/barrier.h
b/arch/s390/include/asm/barrier.h
> index d68e11e..7ffd0b1 100644
> --- a/arch/s390/include/asm/barrier.h
> +++ b/arch/s390/include/asm/barrier.h
> @@ -36,7 +36,7 @@
>  #define smp_mb__before_atomic()		smp_mb()
>  #define smp_mb__after_atomic()		smp_mb()
> 
> -#define smp_store_mb(var, value)		do { WRITE_ONCE(var, value); mb(); }
while (0)
> +#define smp_store_mb(var, value)	do { WRITE_ONCE(var, value); smp_mb(); }
while (0)
> 
>  #define smp_store_release(p, v)						\
>  do {									\
> diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
> index b42afad..0f45f93 100644
> --- a/include/asm-generic/barrier.h
> +++ b/include/asm-generic/barrier.h
> @@ -93,7 +93,7 @@
>  #endif	/* CONFIG_SMP */
> 
>  #ifndef smp_store_mb
> -#define smp_store_mb(var, value)  do { WRITE_ONCE(var, value); mb(); }
while (0)
> +#define smp_store_mb(var, value)  do { WRITE_ONCE(var, value); smp_mb(); }
while (0)
>  #endif
> 
>  #ifndef smp_mb__before_atomic
> -- 
> MST
>

On Sun, Jan 10, 2016 at 04:17:09PM +0200, Michael S. Tsirkin
wrote:
> On powerpc read_barrier_depends, smp_read_barrier_depends
> smp_store_mb(), smp_mb__before_atomic and smp_mb__after_atomic match the
> asm-generic variants exactly. Drop the local definitions and pull in
> asm-generic/barrier.h instead.
> 
> This is in preparation to refactoring this code area.
> 
> Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
> Acked-by: Arnd Bergmann <arnd at arndb.de>
Looks sane to me.

Reviewed-by: Paul E. McKenney <paulmck at linux.vnet.ibm.com>
> ---
>  arch/powerpc/include/asm/barrier.h | 9 ++-------
>  1 file changed, 2 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/barrier.h
b/arch/powerpc/include/asm/barrier.h
> index a7af5fb..980ad0c 100644
> --- a/arch/powerpc/include/asm/barrier.h
> +++ b/arch/powerpc/include/asm/barrier.h
> @@ -34,8 +34,6 @@
>  #define rmb()  __asm__ __volatile__ ("sync" : : :
"memory")
>  #define wmb()  __asm__ __volatile__ ("sync" : : :
"memory")
> 
> -#define smp_store_mb(var, value) do { WRITE_ONCE(var, value); smp_mb(); }
while (0)
> -
>  #ifdef __SUBARCH_HAS_LWSYNC
>  #    define SMPWMB      LWSYNC
>  #else
> @@ -60,9 +58,6 @@
>  #define smp_wmb()	barrier()
>  #endif /* CONFIG_SMP */
> 
> -#define read_barrier_depends()		do { } while (0)
> -#define smp_read_barrier_depends()	do { } while (0)
> -
>  /*
>   * This is a barrier which prevents following instructions from being
>   * started until the value of the argument x is known.  For example, if
> @@ -87,8 +82,8 @@ do {									\
>  	___p1;								\
>  })
> 
> -#define smp_mb__before_atomic()     smp_mb()
> -#define smp_mb__after_atomic()      smp_mb()
>  #define smp_mb__before_spinlock()   smp_mb()
> 
> +#include <asm-generic/barrier.h>
> +
>  #endif /* _ASM_POWERPC_BARRIER_H */
> -- 
> MST
>