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Commit 6addfc42 authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

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: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 37ccdcbe

arch/x86/kvm/x86.c

+26 −10
Original line number Diff line number Diff line
@@ -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);