The pvops function for Xen PV guests handling the interrupt flag are much more complex than needed. With the supported Xen hypervisor versions they can be simplified a lot, especially by removing the need for disabling preemption. Juergen Gross (2): x86/xen: remove xen_have_vcpu_info_placement flag x86/xen: switch initial pvops IRQ functions to dummy ones arch/x86/include/asm/paravirt_types.h | 2 + arch/x86/kernel/paravirt.c | 13 ++- arch/x86/xen/enlighten.c | 116 ++++++-------------------- arch/x86/xen/enlighten_hvm.c | 6 +- arch/x86/xen/enlighten_pv.c | 28 ++----- arch/x86/xen/irq.c | 61 +------------- arch/x86/xen/smp.c | 24 ------ arch/x86/xen/xen-ops.h | 4 +- 8 files changed, 53 insertions(+), 201 deletions(-) -- 2.26.2
Juergen Gross
2021-Sep-22 10:31 UTC
[PATCH v2 2/2] x86/xen: switch initial pvops IRQ functions to dummy ones
The initial pvops functions handling irq flags will only ever be called
before interrupts are being enabled.
So make the __init and switch them to be dummy functions:
- xen_save_fl() can always return 0
- xen_irq_disable() is a nop
- xen_irq_enable() can BUG()
Add some generic paravirt functions for that purpose.
Signed-off-by: Juergen Gross <jgross at suse.com>
---
arch/x86/include/asm/paravirt_types.h | 2 +
arch/x86/kernel/paravirt.c | 13 +++++-
arch/x86/xen/enlighten.c | 19 +--------
arch/x86/xen/irq.c | 61 ++-------------------------
4 files changed, 20 insertions(+), 75 deletions(-)
diff --git a/arch/x86/include/asm/paravirt_types.h
b/arch/x86/include/asm/paravirt_types.h
index d9d6b0203ec4..fc1151e77569 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -577,7 +577,9 @@ void paravirt_leave_lazy_mmu(void);
void paravirt_flush_lazy_mmu(void);
void _paravirt_nop(void);
+void paravirt_BUG(void);
u64 _paravirt_ident_64(u64);
+unsigned long paravirt_ret0(void);
#define paravirt_nop ((void *)_paravirt_nop)
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index 04cafc057bed..4f0ebc46a15d 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -46,6 +46,17 @@ asm (".pushsection .entry.text, \"ax\"\n"
".type _paravirt_nop, @function\n\t"
".popsection");
+/* stub always return ing 0. */
+asm (".pushsection .entry.text, \"ax\"\n"
+ ".global paravirt_ret0\n"
+ "paravirt_ret0:\n\t"
+ "xor %" _ASM_AX ", %" _ASM_AX ";\n\t"
+ "ret\n\t"
+ ".size paravirt_ret0, . - paravirt_ret0\n\t"
+ ".type paravirt_ret0, @function\n\t"
+ ".popsection");
+
+
void __init default_banner(void)
{
printk(KERN_INFO "Booting paravirtualized kernel on %s\n",
@@ -53,7 +64,7 @@ void __init default_banner(void)
}
/* Undefined instruction for dealing with missing ops pointers. */
-static void paravirt_BUG(void)
+void paravirt_BUG(void)
{
BUG();
}
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 8a7bd3f4591e..d96cabe34a01 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -27,25 +27,10 @@ EXPORT_SYMBOL_GPL(hypercall_page);
* Pointer to the xen_vcpu_info structure or
* &HYPERVISOR_shared_info->vcpu_info[cpu]. See xen_hvm_init_shared_info
* and xen_vcpu_setup for details. By default it points to
share_info->vcpu_info
- * but if the hypervisor supports VCPUOP_register_vcpu_info then it can point
- * to xen_vcpu_info. The pointer is used in __xen_evtchn_do_upcall to
- * acknowledge pending events.
- * Also more subtly it is used by the patched version of irq enable/disable
- * e.g. xen_irq_enable_direct and xen_iret in PV mode.
- *
- * The desire to be able to do those mask/unmask operations as a single
- * instruction by using the per-cpu offset held in %gs is the real reason
- * vcpu info is in a per-cpu pointer and the original reason for this
- * hypercall.
- *
+ * but during boot it is switched to point to xen_vcpu_info.
+ * The pointer is used in __xen_evtchn_do_upcall to acknowledge pending events.
*/
DEFINE_PER_CPU(struct vcpu_info *, xen_vcpu);
-
-/*
- * Per CPU pages used if hypervisor supports VCPUOP_register_vcpu_info
- * hypercall. This can be used both in PV and PVHVM mode. The structure
- * overrides the default per_cpu(xen_vcpu, cpu) value.
- */
DEFINE_PER_CPU(struct vcpu_info, xen_vcpu_info);
/* Linux <-> Xen vCPU id mapping */
diff --git a/arch/x86/xen/irq.c b/arch/x86/xen/irq.c
index dfa091d79c2e..ae8537583102 100644
--- a/arch/x86/xen/irq.c
+++ b/arch/x86/xen/irq.c
@@ -24,60 +24,6 @@ void xen_force_evtchn_callback(void)
(void)HYPERVISOR_xen_version(0, NULL);
}
-asmlinkage __visible unsigned long xen_save_fl(void)
-{
- struct vcpu_info *vcpu;
- unsigned long flags;
-
- vcpu = this_cpu_read(xen_vcpu);
-
- /* flag has opposite sense of mask */
- flags = !vcpu->evtchn_upcall_mask;
-
- /* convert to IF type flag
- -0 -> 0x00000000
- -1 -> 0xffffffff
- */
- return (-flags) & X86_EFLAGS_IF;
-}
-PV_CALLEE_SAVE_REGS_THUNK(xen_save_fl);
-
-asmlinkage __visible void xen_irq_disable(void)
-{
- /* There's a one instruction preempt window here. We need to
- make sure we're don't switch CPUs between getting the vcpu
- pointer and updating the mask. */
- preempt_disable();
- this_cpu_read(xen_vcpu)->evtchn_upcall_mask = 1;
- preempt_enable_no_resched();
-}
-PV_CALLEE_SAVE_REGS_THUNK(xen_irq_disable);
-
-asmlinkage __visible void xen_irq_enable(void)
-{
- struct vcpu_info *vcpu;
-
- /*
- * We may be preempted as soon as vcpu->evtchn_upcall_mask is
- * cleared, so disable preemption to ensure we check for
- * events on the VCPU we are still running on.
- */
- preempt_disable();
-
- vcpu = this_cpu_read(xen_vcpu);
- vcpu->evtchn_upcall_mask = 0;
-
- /* Doesn't matter if we get preempted here, because any
- pending event will get dealt with anyway. */
-
- barrier(); /* unmask then check (avoid races) */
- if (unlikely(vcpu->evtchn_upcall_pending))
- xen_force_evtchn_callback();
-
- preempt_enable();
-}
-PV_CALLEE_SAVE_REGS_THUNK(xen_irq_enable);
-
static void xen_safe_halt(void)
{
/* Blocking includes an implicit local_irq_enable(). */
@@ -95,9 +41,10 @@ static void xen_halt(void)
}
static const struct pv_irq_ops xen_irq_ops __initconst = {
- .save_fl = PV_CALLEE_SAVE(xen_save_fl),
- .irq_disable = PV_CALLEE_SAVE(xen_irq_disable),
- .irq_enable = PV_CALLEE_SAVE(xen_irq_enable),
+ /* Initial interrupt flag handling only called while interrupts off. */
+ .save_fl = __PV_IS_CALLEE_SAVE(paravirt_ret0),
+ .irq_disable = __PV_IS_CALLEE_SAVE(paravirt_nop),
+ .irq_enable = __PV_IS_CALLEE_SAVE(paravirt_BUG),
.safe_halt = xen_safe_halt,
.halt = xen_halt,
--
2.26.2
On Wed, Sep 22, 2021 at 12:31:00PM +0200, Juergen Gross wrote:> The pvops function for Xen PV guests handling the interrupt flag are > much more complex than needed. > > With the supported Xen hypervisor versions they can be simplified a > lot, especially by removing the need for disabling preemption. > > Juergen Gross (2): > x86/xen: remove xen_have_vcpu_info_placement flag > x86/xen: switch initial pvops IRQ functions to dummy ones > > arch/x86/include/asm/paravirt_types.h | 2 + > arch/x86/kernel/paravirt.c | 13 ++- > arch/x86/xen/enlighten.c | 116 ++++++-------------------- > arch/x86/xen/enlighten_hvm.c | 6 +- > arch/x86/xen/enlighten_pv.c | 28 ++----- > arch/x86/xen/irq.c | 61 +------------- > arch/x86/xen/smp.c | 24 ------ > arch/x86/xen/xen-ops.h | 4 +- > 8 files changed, 53 insertions(+), 201 deletions(-)That looks awesome, I'm totally in favour of deleting code :-) Acked-by: Peter Zijlstra (Intel) <peterz at infradead.org>