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Commit 2345df8c authored by Avi Kivity's avatar Avi Kivity
Browse files

KVM: VMX: Reduce unnecessary saving of host msrs 



THe automatically switched msrs are never changed on the host (with
the exception of MSR_KERNEL_GS_BASE) and thus there is no need to save
them on every vm entry.

This reduces vmexit latency by ~400 cycles on i386 and by ~900 cycles (10%)
on x86_64.

Signed-off-by: default avatarAvi Kivity <avi@qumranet.com>
parent c9047f53

drivers/kvm/vmx.c

+11 −1
Original line number Diff line number Diff line
@@ -78,6 +78,10 @@ static const u32 vmx_msr_index[] = { 
};

#define NR_VMX_MSR ARRAY_SIZE(vmx_msr_index)



#ifdef CONFIG_X86_64

static unsigned msr_offset_kernel_gs_base;

#endif



static inline int is_page_fault(u32 intr_info)

{

	return (intr_info & (INTR_INFO_INTR_TYPE_MASK | INTR_INFO_VECTOR_MASK |
@@ -1129,6 +1133,10 @@ static int vmx_vcpu_setup(struct kvm_vcpu *vcpu) 
		vcpu->host_msrs[j].reserved = 0;

		vcpu->host_msrs[j].data = data;

		vcpu->guest_msrs[j] = vcpu->host_msrs[j];

#ifdef CONFIG_X86_64

		if (index == MSR_KERNEL_GS_BASE)

			msr_offset_kernel_gs_base = j;

#endif

		++vcpu->nmsrs;

	}
@@ -1760,7 +1768,9 @@ static int vmx_vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run) 
	fx_save(vcpu->host_fx_image);

	fx_restore(vcpu->guest_fx_image);



	save_msrs(vcpu->host_msrs, vcpu->nmsrs);

#ifdef CONFIG_X86_64

	save_msrs(vcpu->host_msrs + msr_offset_kernel_gs_base, 1);

#endif

	load_msrs(vcpu->guest_msrs, NR_BAD_MSRS);



	asm (