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KVM: x86: avoid useless set of KVM_REQ_EVENT after emulation

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Despite the provisions to emulate up to 130 consecutive instructions, in
practice KVM will emulate just one before exiting handle_invalid_guest_state,
because x86_emulate_instruction always sets KVM_REQ_EVENT.

However, we only need to do this if an interrupt could be injected,
which happens a) if an interrupt shadow bit (STI or MOV SS) has gone
away; b) if the interrupt flag has just been set (other instructions
than STI can set it without enabling an interrupt shadow).

This cuts another 700-900 cycles from the cost of emulating an
instruction (measured on a Sandy Bridge Xeon: 1650-2600 cycles
before the patch on kvm-unit-tests, 925-1700 afterwards).

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2014-03-27 11:29:28 +01:00
parent 37ccdcbe07
commit 6addfc4299
1 changed files with 26 additions and 10 deletions
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36
arch/x86/kvm/x86.c
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@ -87,6 +87,7 @@ static u64 __read_mostly efer_reserved_bits = ~((u64)EFER_SCE);
static void update_cr8_intercept(struct kvm_vcpu *vcpu);
static void process_nmi(struct kvm_vcpu *vcpu);
static void __kvm_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags);
struct kvm_x86_ops *kvm_x86_ops;
EXPORT_SYMBOL_GPL(kvm_x86_ops);
@ -4868,8 +4869,11 @@ static void toggle_interruptibility(struct kvm_vcpu *vcpu, u32 mask)
*/
if (int_shadow & mask)
mask = 0;
if (unlikely(int_shadow || mask))
if (unlikely(int_shadow || mask)) {
kvm_x86_ops->set_interrupt_shadow(vcpu, mask);
if (!mask)
kvm_make_request(KVM_REQ_EVENT, vcpu);
}
}
static void inject_emulated_exception(struct kvm_vcpu *vcpu)
@ -5095,20 +5099,18 @@ static int kvm_vcpu_check_hw_bp(unsigned long addr, u32 type, u32 dr7,
return dr6;
}
static void kvm_vcpu_check_singlestep(struct kvm_vcpu *vcpu, int *r)
static void kvm_vcpu_check_singlestep(struct kvm_vcpu *vcpu, unsigned long rflags, int *r)
{
struct kvm_run *kvm_run = vcpu->run;
/*
* Use the "raw" value to see if TF was passed to the processor.
* Note that the new value of the flags has not been saved yet.
* rflags is the old, "raw" value of the flags. The new value has
* not been saved yet.
*
* This is correct even for TF set by the guest, because "the
* processor will not generate this exception after the instruction
* that sets the TF flag".
*/
unsigned long rflags = kvm_x86_ops->get_rflags(vcpu);
if (unlikely(rflags & X86_EFLAGS_TF)) {
if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
kvm_run->debug.arch.dr6 = DR6_BS | DR6_FIXED_1;
@ -5275,13 +5277,22 @@ restart:
r = EMULATE_DONE;
if (writeback) {
unsigned long rflags = kvm_x86_ops->get_rflags(vcpu);
toggle_interruptibility(vcpu, ctxt->interruptibility);
kvm_make_request(KVM_REQ_EVENT, vcpu);
vcpu->arch.emulate_regs_need_sync_to_vcpu = false;
kvm_rip_write(vcpu, ctxt->eip);
if (r == EMULATE_DONE)
kvm_vcpu_check_singlestep(vcpu, &r);
kvm_set_rflags(vcpu, ctxt->eflags);
kvm_vcpu_check_singlestep(vcpu, rflags, &r);
__kvm_set_rflags(vcpu, ctxt->eflags);
/*
* For STI, interrupts are shadowed; so KVM_REQ_EVENT will
* do nothing, and it will be requested again as soon as
* the shadow expires. But we still need to check here,
* because POPF has no interrupt shadow.
*/
if (unlikely((ctxt->eflags & ~rflags) & X86_EFLAGS_IF))
kvm_make_request(KVM_REQ_EVENT, vcpu);
} else
vcpu->arch.emulate_regs_need_sync_to_vcpu = true;
@ -7406,12 +7417,17 @@ unsigned long kvm_get_rflags(struct kvm_vcpu *vcpu)
}
EXPORT_SYMBOL_GPL(kvm_get_rflags);
void kvm_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
static void __kvm_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
{
if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP &&
kvm_is_linear_rip(vcpu, vcpu->arch.singlestep_rip))
rflags |= X86_EFLAGS_TF;
kvm_x86_ops->set_rflags(vcpu, rflags);
}
void kvm_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags)
{
__kvm_set_rflags(vcpu, rflags);
kvm_make_request(KVM_REQ_EVENT, vcpu);
}
EXPORT_SYMBOL_GPL(kvm_set_rflags);