From 6addfc42992be4b073c39137ecfdf4b2aa2d487f Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Thu, 27 Mar 2014 11:29:28 +0100 Subject: [PATCH] KVM: x86: avoid useless set of KVM_REQ_EVENT after emulation 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 --- arch/x86/kvm/x86.c | 36 ++++++++++++++++++++++++++---------- 1 file changed, 26 insertions(+), 10 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index a56126e6bd75..cd9316786dca 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -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); -- 2.20.1