thr3ads.net - Linux Virtualization - [PATCH v2 1/3] x86/xen: Avoid fast syscall path for Xen PV guests [Dec 2015]

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Boris Ostrovsky

2015-Nov-19 21:55 UTC

[PATCH v2 0/3] Fix and cleanup for 32-bit PV sysexit

The first patch fixes Xen PV regression introduced by 32-bit rewrite. Unlike the
earlier version it uses ALTERNATIVE instruction and avoids using xen_sysexit
(and sysret32 in compat mode) pv ops, as suggested by Andy.

As result of this patch irq_enable_sysexit and usergs_sysret32 pv ops are not
used anymore by anyone and so can be removed.


v2:
  * patch both TEST and JZ intructions with a single JMP
  * Add magic prefix to X86_FEATURE_XENPV comment to avoid having it printed in
    /proc/cpuinfo
  * Clarify in commit messages why irq_enable_sysexit and usergs_sysret32 are
    removed


Boris Ostrovsky (3):
  x86/xen: Avoid fast syscall path for Xen PV guests
  x86: irq_enable_sysexit pv op is no longer needed
  x86: usergs_sysret32 pv op is no longer needed

 arch/x86/entry/entry_32.S             | 13 +++++--------
 arch/x86/entry/entry_64_compat.S      | 20 ++++++++------------
 arch/x86/include/asm/cpufeature.h     |  1 +
 arch/x86/include/asm/paravirt.h       | 12 ------------
 arch/x86/include/asm/paravirt_types.h | 17 -----------------
 arch/x86/kernel/asm-offsets.c         |  3 ---
 arch/x86/kernel/asm-offsets_64.c      |  1 -
 arch/x86/kernel/paravirt.c            | 12 ------------
 arch/x86/kernel/paravirt_patch_32.c   |  2 --
 arch/x86/kernel/paravirt_patch_64.c   |  3 ---
 arch/x86/xen/enlighten.c              |  7 +++----
 arch/x86/xen/xen-asm_32.S             | 14 --------------
 arch/x86/xen/xen-asm_64.S             | 19 -------------------
 arch/x86/xen/xen-ops.h                |  3 ---
 14 files changed, 17 insertions(+), 110 deletions(-)

-- 
1.8.1.4

Boris Ostrovsky

2015-Nov-19 21:55 UTC

head link

[PATCH v2 1/3] x86/xen: Avoid fast syscall path for Xen PV guests

After 32-bit syscall rewrite, and specifically after commit 5f310f739b4c
("x86/entry/32: Re-implement SYSENTER using the new C path"), the
stack
frame that is passed to xen_sysexit is no longer a "standard" one
(i.e.
it's not pt_regs).

Since we end up calling xen_iret from xen_sysexit we don't need to fix
up the stack and instead follow entry_SYSENTER_32's IRET path directly
to xen_iret.

We can do the same thing for compat mode even though stack does not need
to be fixed. This will allow us to drop usergs_sysret32 paravirt op (in
the subsequent patch)

Signed-off-by: Boris Ostrovsky <boris.ostrovsky at oracle.com>
Suggested-by: Andy Lutomirski <luto at amacapital.net>
---
 arch/x86/entry/entry_32.S         |  5 +++--
 arch/x86/entry/entry_64_compat.S  | 10 ++++++----
 arch/x86/include/asm/cpufeature.h |  1 +
 arch/x86/xen/enlighten.c          |  4 +++-
 4 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 3eb572e..0870825 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -308,8 +308,9 @@ sysenter_past_esp:
 
 	movl	%esp, %eax
 	call	do_fast_syscall_32
-	testl	%eax, %eax
-	jz	.Lsyscall_32_done
+	/* XEN PV guests always use IRET path */
+	ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \
+		    "jmp .Lsyscall_32_done", X86_FEATURE_XENPV
 
 /* Opportunistic SYSEXIT */
 	TRACE_IRQS_ON			/* User mode traces as IRQs on. */
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index c320183..402e34a 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -121,8 +121,9 @@ sysenter_flags_fixed:
 
 	movq	%rsp, %rdi
 	call	do_fast_syscall_32
-	testl	%eax, %eax
-	jz	.Lsyscall_32_done
+	/* XEN PV guests always use IRET path */
+	ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \
+		    "jmp .Lsyscall_32_done", X86_FEATURE_XENPV
 	jmp	sysret32_from_system_call
 
 sysenter_fix_flags:
@@ -200,8 +201,9 @@ ENTRY(entry_SYSCALL_compat)
 
 	movq	%rsp, %rdi
 	call	do_fast_syscall_32
-	testl	%eax, %eax
-	jz	.Lsyscall_32_done
+	/* XEN PV guests always use IRET path */
+	ALTERNATIVE "testl %eax, %eax; jz .Lsyscall_32_done", \
+		    "jmp .Lsyscall_32_done", X86_FEATURE_XENPV
 
 	/* Opportunistic SYSRET */
 sysret32_from_system_call:
diff --git a/arch/x86/include/asm/cpufeature.h
b/arch/x86/include/asm/cpufeature.h
index e4f8010..f7ba9fb 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -216,6 +216,7 @@
 #define X86_FEATURE_PAUSEFILTER ( 8*32+13) /* AMD filtered pause intercept */
 #define X86_FEATURE_PFTHRESHOLD ( 8*32+14) /* AMD pause filter threshold */
 #define X86_FEATURE_VMMCALL     ( 8*32+15) /* Prefer vmmcall to vmcall */
+#define X86_FEATURE_XENPV       ( 8*32+16) /* "" Xen paravirtual
guest */
 
 
 /* Intel-defined CPU features, CPUID level 0x00000007:0 (ebx), word 9 */
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 5774800..d315151 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1886,8 +1886,10 @@ EXPORT_SYMBOL_GPL(xen_hvm_need_lapic);
 
 static void xen_set_cpu_features(struct cpuinfo_x86 *c)
 {
-	if (xen_pv_domain())
+	if (xen_pv_domain()) {
 		clear_cpu_bug(c, X86_BUG_SYSRET_SS_ATTRS);
+		set_cpu_cap(c, X86_FEATURE_XENPV);
+	}
 }
 
 const struct hypervisor_x86 x86_hyper_xen = {
-- 
1.8.1.4

Boris Ostrovsky

2015-Nov-19 21:55 UTC

head link

[PATCH v2 2/3] x86: irq_enable_sysexit pv op is no longer needed

As result of commit "x86/xen: Avoid fast syscall path for Xen PV
guests"
irq_enable_sysexit pv op is not called by Xen PV guests anymore and since
they were the only ones who used it we can safely remove it.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky at oracle.com>
---
 arch/x86/entry/entry_32.S             |  8 ++------
 arch/x86/include/asm/paravirt.h       |  7 -------
 arch/x86/include/asm/paravirt_types.h |  9 ---------
 arch/x86/kernel/asm-offsets.c         |  3 ---
 arch/x86/kernel/paravirt.c            |  7 -------
 arch/x86/kernel/paravirt_patch_32.c   |  2 --
 arch/x86/kernel/paravirt_patch_64.c   |  1 -
 arch/x86/xen/enlighten.c              |  3 ---
 arch/x86/xen/xen-asm_32.S             | 14 --------------
 arch/x86/xen/xen-ops.h                |  3 ---
 10 files changed, 2 insertions(+), 55 deletions(-)

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 0870825..9870c97 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -329,7 +329,8 @@ sysenter_past_esp:
 	 * Return back to the vDSO, which will pop ecx and edx.
 	 * Don't bother with DS and ES (they already contain __USER_DS).
 	 */
-	ENABLE_INTERRUPTS_SYSEXIT
+	sti
+	sysexit
 
 .pushsection .fixup, "ax"
 2:	movl	$0, PT_FS(%esp)
@@ -552,11 +553,6 @@ ENTRY(native_iret)
 	iret
 	_ASM_EXTABLE(native_iret, iret_exc)
 END(native_iret)
-
-ENTRY(native_irq_enable_sysexit)
-	sti
-	sysexit
-END(native_irq_enable_sysexit)
 #endif
 
 ENTRY(overflow)
diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 10d0596..c28518e 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -932,13 +932,6 @@ extern void default_banner(void);
 	push %ecx; push %edx;				\
 	call PARA_INDIRECT(pv_cpu_ops+PV_CPU_read_cr0);	\
 	pop %edx; pop %ecx
-
-#define ENABLE_INTERRUPTS_SYSEXIT					\
-	PARA_SITE(PARA_PATCH(pv_cpu_ops, PV_CPU_irq_enable_sysexit),	\
-		  CLBR_NONE,						\
-		  jmp PARA_INDIRECT(pv_cpu_ops+PV_CPU_irq_enable_sysexit))
-
-
 #else	/* !CONFIG_X86_32 */
 
 /*
diff --git a/arch/x86/include/asm/paravirt_types.h
b/arch/x86/include/asm/paravirt_types.h
index 31247b5..608bbf3 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -157,15 +157,6 @@ struct pv_cpu_ops {
 
 	u64 (*read_pmc)(int counter);
 
-#ifdef CONFIG_X86_32
-	/*
-	 * Atomically enable interrupts and return to userspace.  This
-	 * is only used in 32-bit kernels.  64-bit kernels use
-	 * usergs_sysret32 instead.
-	 */
-	void (*irq_enable_sysexit)(void);
-#endif
-
 	/*
 	 * Switch to usermode gs and return to 64-bit usermode using
 	 * sysret.  Only used in 64-bit kernels to return to 64-bit
diff --git a/arch/x86/kernel/asm-offsets.c b/arch/x86/kernel/asm-offsets.c
index 439df97..84a7524 100644
--- a/arch/x86/kernel/asm-offsets.c
+++ b/arch/x86/kernel/asm-offsets.c
@@ -65,9 +65,6 @@ void common(void) {
 	OFFSET(PV_IRQ_irq_disable, pv_irq_ops, irq_disable);
 	OFFSET(PV_IRQ_irq_enable, pv_irq_ops, irq_enable);
 	OFFSET(PV_CPU_iret, pv_cpu_ops, iret);
-#ifdef CONFIG_X86_32
-	OFFSET(PV_CPU_irq_enable_sysexit, pv_cpu_ops, irq_enable_sysexit);
-#endif
 	OFFSET(PV_CPU_read_cr0, pv_cpu_ops, read_cr0);
 	OFFSET(PV_MMU_read_cr2, pv_mmu_ops, read_cr2);
 #endif
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index c2130ae..c55f437 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -162,9 +162,6 @@ unsigned paravirt_patch_default(u8 type, u16 clobbers, void
*insnbuf,
 		ret = paravirt_patch_ident_64(insnbuf, len);
 
 	else if (type == PARAVIRT_PATCH(pv_cpu_ops.iret) ||
-#ifdef CONFIG_X86_32
-		 type == PARAVIRT_PATCH(pv_cpu_ops.irq_enable_sysexit) ||
-#endif
 		 type == PARAVIRT_PATCH(pv_cpu_ops.usergs_sysret32) ||
 		 type == PARAVIRT_PATCH(pv_cpu_ops.usergs_sysret64))
 		/* If operation requires a jmp, then jmp */
@@ -220,7 +217,6 @@ static u64 native_steal_clock(int cpu)
 
 /* These are in entry.S */
 extern void native_iret(void);
-extern void native_irq_enable_sysexit(void);
 extern void native_usergs_sysret32(void);
 extern void native_usergs_sysret64(void);
 
@@ -379,9 +375,6 @@ __visible struct pv_cpu_ops pv_cpu_ops = {
 
 	.load_sp0 = native_load_sp0,
 
-#if defined(CONFIG_X86_32)
-	.irq_enable_sysexit = native_irq_enable_sysexit,
-#endif
 #ifdef CONFIG_X86_64
 #ifdef CONFIG_IA32_EMULATION
 	.usergs_sysret32 = native_usergs_sysret32,
diff --git a/arch/x86/kernel/paravirt_patch_32.c
b/arch/x86/kernel/paravirt_patch_32.c
index c89f50a..158dc06 100644
--- a/arch/x86/kernel/paravirt_patch_32.c
+++ b/arch/x86/kernel/paravirt_patch_32.c
@@ -5,7 +5,6 @@ DEF_NATIVE(pv_irq_ops, irq_enable, "sti");
 DEF_NATIVE(pv_irq_ops, restore_fl, "push %eax; popf");
 DEF_NATIVE(pv_irq_ops, save_fl, "pushf; pop %eax");
 DEF_NATIVE(pv_cpu_ops, iret, "iret");
-DEF_NATIVE(pv_cpu_ops, irq_enable_sysexit, "sti; sysexit");
 DEF_NATIVE(pv_mmu_ops, read_cr2, "mov %cr2, %eax");
 DEF_NATIVE(pv_mmu_ops, write_cr3, "mov %eax, %cr3");
 DEF_NATIVE(pv_mmu_ops, read_cr3, "mov %cr3, %eax");
@@ -46,7 +45,6 @@ unsigned native_patch(u8 type, u16 clobbers, void *ibuf,
 		PATCH_SITE(pv_irq_ops, restore_fl);
 		PATCH_SITE(pv_irq_ops, save_fl);
 		PATCH_SITE(pv_cpu_ops, iret);
-		PATCH_SITE(pv_cpu_ops, irq_enable_sysexit);
 		PATCH_SITE(pv_mmu_ops, read_cr2);
 		PATCH_SITE(pv_mmu_ops, read_cr3);
 		PATCH_SITE(pv_mmu_ops, write_cr3);
diff --git a/arch/x86/kernel/paravirt_patch_64.c
b/arch/x86/kernel/paravirt_patch_64.c
index 8aa0558..17c00f8 100644
--- a/arch/x86/kernel/paravirt_patch_64.c
+++ b/arch/x86/kernel/paravirt_patch_64.c
@@ -13,7 +13,6 @@ DEF_NATIVE(pv_mmu_ops, flush_tlb_single, "invlpg
(%rdi)");
 DEF_NATIVE(pv_cpu_ops, clts, "clts");
 DEF_NATIVE(pv_cpu_ops, wbinvd, "wbinvd");
 
-DEF_NATIVE(pv_cpu_ops, irq_enable_sysexit, "swapgs; sti; sysexit");
 DEF_NATIVE(pv_cpu_ops, usergs_sysret64, "swapgs; sysretq");
 DEF_NATIVE(pv_cpu_ops, usergs_sysret32, "swapgs; sysretl");
 DEF_NATIVE(pv_cpu_ops, swapgs, "swapgs");
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index d315151..a068e36 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1229,10 +1229,7 @@ static const struct pv_cpu_ops xen_cpu_ops __initconst =
{
 
 	.iret = xen_iret,
 #ifdef CONFIG_X86_64
-	.usergs_sysret32 = xen_sysret32,
 	.usergs_sysret64 = xen_sysret64,
-#else
-	.irq_enable_sysexit = xen_sysexit,
 #endif
 
 	.load_tr_desc = paravirt_nop,
diff --git a/arch/x86/xen/xen-asm_32.S b/arch/x86/xen/xen-asm_32.S
index fd92a64..feb6d40 100644
--- a/arch/x86/xen/xen-asm_32.S
+++ b/arch/x86/xen/xen-asm_32.S
@@ -35,20 +35,6 @@ check_events:
 	ret
 
 /*
- * We can't use sysexit directly, because we're not running in ring0.
- * But we can easily fake it up using iret.  Assuming xen_sysexit is
- * jumped to with a standard stack frame, we can just strip it back to
- * a standard iret frame and use iret.
- */
-ENTRY(xen_sysexit)
-	movl PT_EAX(%esp), %eax			/* Shouldn't be necessary? */
-	orl $X86_EFLAGS_IF, PT_EFLAGS(%esp)
-	lea PT_EIP(%esp), %esp
-
-	jmp xen_iret
-ENDPROC(xen_sysexit)
-
-/*
  * This is run where a normal iret would be run, with the same stack setup:
  *	8: eflags
  *	4: cs
diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
index 1399423..4140b07 100644
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@@ -139,9 +139,6 @@ DECL_ASM(void, xen_restore_fl_direct, unsigned long);
 
 /* These are not functions, and cannot be called normally */
 __visible void xen_iret(void);
-#ifdef CONFIG_X86_32
-__visible void xen_sysexit(void);
-#endif
 __visible void xen_sysret32(void);
 __visible void xen_sysret64(void);
 __visible void xen_adjust_exception_frame(void);
-- 
1.8.1.4

Boris Ostrovsky

2015-Nov-19 21:55 UTC

head link

[PATCH v2 3/3] x86: usergs_sysret32 pv op is no longer needed

As result of commit "x86/xen: Avoid fast syscall path for Xen PV
guests"
usergs_sysret32 pv op is not called by Xen PV guests anymore and
since they were the only ones who used it we can safely remove it.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky at oracle.com>
---
 arch/x86/entry/entry_64_compat.S      | 10 ++--------
 arch/x86/include/asm/paravirt.h       |  5 -----
 arch/x86/include/asm/paravirt_types.h |  8 --------
 arch/x86/kernel/asm-offsets_64.c      |  1 -
 arch/x86/kernel/paravirt.c            |  5 -----
 arch/x86/kernel/paravirt_patch_64.c   |  2 --
 arch/x86/xen/xen-asm_64.S             | 19 -------------------
 7 files changed, 2 insertions(+), 48 deletions(-)

diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index 402e34a..bbcb285 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -18,13 +18,6 @@
 
 	.section .entry.text, "ax"
 
-#ifdef CONFIG_PARAVIRT
-ENTRY(native_usergs_sysret32)
-	swapgs
-	sysretl
-ENDPROC(native_usergs_sysret32)
-#endif
-
 /*
  * 32-bit SYSENTER instruction entry.
  *
@@ -238,7 +231,8 @@ sysret32_from_system_call:
 	xorq	%r9, %r9
 	xorq	%r10, %r10
 	movq	RSP-ORIG_RAX(%rsp), %rsp
-        USERGS_SYSRET32
+	swapgs
+	sysretl
 END(entry_SYSCALL_compat)
 
 /*
diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index c28518e..1b71c3a 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -922,11 +922,6 @@ extern void default_banner(void);
 		  call PARA_INDIRECT(pv_irq_ops+PV_IRQ_irq_enable);	\
 		  PV_RESTORE_REGS(clobbers | CLBR_CALLEE_SAVE);)
 
-#define USERGS_SYSRET32							\
-	PARA_SITE(PARA_PATCH(pv_cpu_ops, PV_CPU_usergs_sysret32),	\
-		  CLBR_NONE,						\
-		  jmp PARA_INDIRECT(pv_cpu_ops+PV_CPU_usergs_sysret32))
-
 #ifdef CONFIG_X86_32
 #define GET_CR0_INTO_EAX				\
 	push %ecx; push %edx;				\
diff --git a/arch/x86/include/asm/paravirt_types.h
b/arch/x86/include/asm/paravirt_types.h
index 608bbf3..702c8bd 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -165,14 +165,6 @@ struct pv_cpu_ops {
 	 */
 	void (*usergs_sysret64)(void);
 
-	/*
-	 * Switch to usermode gs and return to 32-bit usermode using
-	 * sysret.  Used to return to 32-on-64 compat processes.
-	 * Other usermode register state, including %esp, must already
-	 * be restored.
-	 */
-	void (*usergs_sysret32)(void);
-
 	/* Normal iret.  Jump to this with the standard iret stack
 	   frame set up. */
 	void (*iret)(void);
diff --git a/arch/x86/kernel/asm-offsets_64.c b/arch/x86/kernel/asm-offsets_64.c
index d8f42f9..f2edafb 100644
--- a/arch/x86/kernel/asm-offsets_64.c
+++ b/arch/x86/kernel/asm-offsets_64.c
@@ -23,7 +23,6 @@ int main(void)
 {
 #ifdef CONFIG_PARAVIRT
 	OFFSET(PV_IRQ_adjust_exception_frame, pv_irq_ops, adjust_exception_frame);
-	OFFSET(PV_CPU_usergs_sysret32, pv_cpu_ops, usergs_sysret32);
 	OFFSET(PV_CPU_usergs_sysret64, pv_cpu_ops, usergs_sysret64);
 	OFFSET(PV_CPU_swapgs, pv_cpu_ops, swapgs);
 	BLANK();
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index c55f437..8c19b4d 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -162,7 +162,6 @@ unsigned paravirt_patch_default(u8 type, u16 clobbers, void
*insnbuf,
 		ret = paravirt_patch_ident_64(insnbuf, len);
 
 	else if (type == PARAVIRT_PATCH(pv_cpu_ops.iret) ||
-		 type == PARAVIRT_PATCH(pv_cpu_ops.usergs_sysret32) ||
 		 type == PARAVIRT_PATCH(pv_cpu_ops.usergs_sysret64))
 		/* If operation requires a jmp, then jmp */
 		ret = paravirt_patch_jmp(insnbuf, opfunc, addr, len);
@@ -217,7 +216,6 @@ static u64 native_steal_clock(int cpu)
 
 /* These are in entry.S */
 extern void native_iret(void);
-extern void native_usergs_sysret32(void);
 extern void native_usergs_sysret64(void);
 
 static struct resource reserve_ioports = {
@@ -376,9 +374,6 @@ __visible struct pv_cpu_ops pv_cpu_ops = {
 	.load_sp0 = native_load_sp0,
 
 #ifdef CONFIG_X86_64
-#ifdef CONFIG_IA32_EMULATION
-	.usergs_sysret32 = native_usergs_sysret32,
-#endif
 	.usergs_sysret64 = native_usergs_sysret64,
 #endif
 	.iret = native_iret,
diff --git a/arch/x86/kernel/paravirt_patch_64.c
b/arch/x86/kernel/paravirt_patch_64.c
index 17c00f8..e70087a 100644
--- a/arch/x86/kernel/paravirt_patch_64.c
+++ b/arch/x86/kernel/paravirt_patch_64.c
@@ -14,7 +14,6 @@ DEF_NATIVE(pv_cpu_ops, clts, "clts");
 DEF_NATIVE(pv_cpu_ops, wbinvd, "wbinvd");
 
 DEF_NATIVE(pv_cpu_ops, usergs_sysret64, "swapgs; sysretq");
-DEF_NATIVE(pv_cpu_ops, usergs_sysret32, "swapgs; sysretl");
 DEF_NATIVE(pv_cpu_ops, swapgs, "swapgs");
 
 DEF_NATIVE(, mov32, "mov %edi, %eax");
@@ -54,7 +53,6 @@ unsigned native_patch(u8 type, u16 clobbers, void *ibuf,
 		PATCH_SITE(pv_irq_ops, save_fl);
 		PATCH_SITE(pv_irq_ops, irq_enable);
 		PATCH_SITE(pv_irq_ops, irq_disable);
-		PATCH_SITE(pv_cpu_ops, usergs_sysret32);
 		PATCH_SITE(pv_cpu_ops, usergs_sysret64);
 		PATCH_SITE(pv_cpu_ops, swapgs);
 		PATCH_SITE(pv_mmu_ops, read_cr2);
diff --git a/arch/x86/xen/xen-asm_64.S b/arch/x86/xen/xen-asm_64.S
index f22667a..cc8acc4 100644
--- a/arch/x86/xen/xen-asm_64.S
+++ b/arch/x86/xen/xen-asm_64.S
@@ -68,25 +68,6 @@ ENTRY(xen_sysret64)
 ENDPATCH(xen_sysret64)
 RELOC(xen_sysret64, 1b+1)
 
-ENTRY(xen_sysret32)
-	/*
-	 * We're already on the usermode stack at this point, but
-	 * still with the kernel gs, so we can easily switch back
-	 */
-	movq %rsp, PER_CPU_VAR(rsp_scratch)
-	movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
-
-	pushq $__USER32_DS
-	pushq PER_CPU_VAR(rsp_scratch)
-	pushq %r11
-	pushq $__USER32_CS
-	pushq %rcx
-
-	pushq $0
-1:	jmp hypercall_iret
-ENDPATCH(xen_sysret32)
-RELOC(xen_sysret32, 1b+1)
-
 /*
  * Xen handles syscall callbacks much like ordinary exceptions, which
  * means we have:
-- 
1.8.1.4

Andy Lutomirski

2015-Nov-19 22:07 UTC

head link

[PATCH v2 0/3] Fix and cleanup for 32-bit PV sysexit

On Thu, Nov 19, 2015 at 1:55 PM, Boris Ostrovsky
<boris.ostrovsky at oracle.com> wrote:> The first patch fixes Xen PV regression introduced by 32-bit rewrite.
Unlike the
> earlier version it uses ALTERNATIVE instruction and avoids using
xen_sysexit
> (and sysret32 in compat mode) pv ops, as suggested by Andy.
>
> As result of this patch irq_enable_sysexit and usergs_sysret32 pv ops are
not
> used anymore by anyone and so can be removed.
This whole series is:

Acked-by: Andy Lutomirski <luto at kernel.org>

Now I just have to sucker someone into getting rid of
PARAVIRT_ADJUST_EXCEPTION_FRAME (by using stub entries) and the
overcomplicated syscall entry stuff.  :)  And whoever gets rid of
PARAVIRT_ADJUST_EXCEPTION_FRAME gets to wonder why it doesn't crash
and burn for NMIs on Xen, since I'm reasonably confident that it can't
possibly be correct.

--Andy

Borislav Petkov

2015-Nov-19 23:02 UTC

head link

[PATCH v2 0/3] Fix and cleanup for 32-bit PV sysexit

On Thu, Nov 19, 2015 at 04:55:44PM -0500, Boris Ostrovsky
wrote:> The first patch fixes Xen PV regression introduced by 32-bit rewrite.
Unlike the
> earlier version it uses ALTERNATIVE instruction and avoids using
xen_sysexit
> (and sysret32 in compat mode) pv ops, as suggested by Andy.
> 
> As result of this patch irq_enable_sysexit and usergs_sysret32 pv ops are
not
> used anymore by anyone and so can be removed.
> 
> 
> v2:
>   * patch both TEST and JZ intructions with a single JMP
>   * Add magic prefix to X86_FEATURE_XENPV comment to avoid having it
printed in
>     /proc/cpuinfo
>   * Clarify in commit messages why irq_enable_sysexit and usergs_sysret32
are
>     removed
> 
> 
> Boris Ostrovsky (3):
>   x86/xen: Avoid fast syscall path for Xen PV guests
>   x86: irq_enable_sysexit pv op is no longer needed
>   x86: usergs_sysret32 pv op is no longer needed
> 
>  arch/x86/entry/entry_32.S             | 13 +++++--------
>  arch/x86/entry/entry_64_compat.S      | 20 ++++++++------------
>  arch/x86/include/asm/cpufeature.h     |  1 +
>  arch/x86/include/asm/paravirt.h       | 12 ------------
>  arch/x86/include/asm/paravirt_types.h | 17 -----------------
>  arch/x86/kernel/asm-offsets.c         |  3 ---
>  arch/x86/kernel/asm-offsets_64.c      |  1 -
>  arch/x86/kernel/paravirt.c            | 12 ------------
>  arch/x86/kernel/paravirt_patch_32.c   |  2 --
>  arch/x86/kernel/paravirt_patch_64.c   |  3 ---
>  arch/x86/xen/enlighten.c              |  7 +++----
>  arch/x86/xen/xen-asm_32.S             | 14 --------------
>  arch/x86/xen/xen-asm_64.S             | 19 -------------------
>  arch/x86/xen/xen-ops.h                |  3 ---
>  14 files changed, 17 insertions(+), 110 deletions(-)
All three look good to me.

Reviewed-by: Borislav Petkov <bp at suse.de>

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imend?rffer, Jane Smithard, Graham Norton, HRB 21284
(AG N?rnberg)
--

Boris Ostrovsky

2015-Dec-15 15:21 UTC

head link

[PATCH v2 1/3] x86/xen: Avoid fast syscall path for Xen PV guests

On 11/19/2015 04:55 PM, Boris Ostrovsky wrote:> After 32-bit syscall rewrite, and specifically after commit 5f310f739b4c
> ("x86/entry/32: Re-implement SYSENTER using the new C path"), the
stack
> frame that is passed to xen_sysexit is no longer a "standard" one
(i.e.
> it's not pt_regs).
>
> Since we end up calling xen_iret from xen_sysexit we don't need to fix
> up the stack and instead follow entry_SYSENTER_32's IRET path directly
> to xen_iret.
>
> We can do the same thing for compat mode even though stack does not need
> to be fixed. This will allow us to drop usergs_sysret32 paravirt op (in
> the subsequent patch)
>
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky at oracle.com>
> Suggested-by: Andy Lutomirski <luto at amacapital.net>

I know this has been in the tip tree --- when do you think this will go 
Linus tree? In the 4.4 timeframe?

Xen 32-bit PV guests are broken without this.


Thanks.
-boris

Andrew Cooper

2015-Dec-15 20:40 UTC

head link

[Xen-devel] [PATCH v2 0/3] Fix and cleanup for 32-bit PV sysexit

On 19/11/15 22:07, Andy Lutomirski wrote:> On Thu, Nov 19, 2015 at 1:55 PM, Boris Ostrovsky
> <boris.ostrovsky at oracle.com> wrote:
>> The first patch fixes Xen PV regression introduced by 32-bit rewrite.
Unlike the
>> earlier version it uses ALTERNATIVE instruction and avoids using
xen_sysexit
>> (and sysret32 in compat mode) pv ops, as suggested by Andy.
>>
>> As result of this patch irq_enable_sysexit and usergs_sysret32 pv ops
are not
>> used anymore by anyone and so can be removed.
> This whole series is:
>
> Acked-by: Andy Lutomirski <luto at kernel.org>
>
> Now I just have to sucker someone into getting rid of
> PARAVIRT_ADJUST_EXCEPTION_FRAME (by using stub entries) and the
> overcomplicated syscall entry stuff.  :)
Looking at this, it should be quite easy now.

ALTERNATIVE "", "pop %rcx; %pop %11", X86_FEATURE_XENPV

(Completely untested)
> And whoever gets rid of
> PARAVIRT_ADJUST_EXCEPTION_FRAME gets to wonder why it doesn't crash
> and burn for NMIs on Xen, since I'm reasonably confident that it
can't
> possibly be correct.
The Xen PV ABI only has a single kernel stack pointer which may be
registered.  There is no equivalent of an IST, so if a second fault
occurs, it is delivered normally on the current stack.

By the looks of it, the other NMI handling is ambivalent to the fact
that it isn't really on an IST stack under Xen.

~Andrew

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