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KVM: VMX: Reduce unnecessary saving of host msrs

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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: Avi Kivity <avi@qumranet.com>
This commit is contained in:
Avi Kivity
2007-04-17 15:30:24 +03:00
parent c9047f5333
commit 2345df8c55
1 changed files with 11 additions and 1 deletions
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12
drivers/kvm/vmx.c
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@@ -78,6 +78,10 @@ static const u32 vmx_msr_index[] = {
}; };
#define NR_VMX_MSR ARRAY_SIZE(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) static inline int is_page_fault(u32 intr_info)
{ {
return (intr_info & (INTR_INFO_INTR_TYPE_MASK | INTR_INFO_VECTOR_MASK | 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].reserved = 0;
vcpu->host_msrs[j].data = data; vcpu->host_msrs[j].data = data;
vcpu->guest_msrs[j] = vcpu->host_msrs[j]; 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; ++vcpu->nmsrs;
} }
@@ -1760,7 +1768,9 @@ again:
fx_save(vcpu->host_fx_image); fx_save(vcpu->host_fx_image);
fx_restore(vcpu->guest_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); load_msrs(vcpu->guest_msrs, NR_BAD_MSRS);
asm ( asm (