Re: [PATCH] KVM: x86: avoid unnecessary XSETBV on guest entry
From: Quan Xu
Date: Wed Dec 13 2017 - 22:27:40 EST
On 2017/12/13 20:51, Paolo Bonzini wrote:
xsetbv can be expensive when running on nested virtualization, try to
avoid it.
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
arch/x86/kvm/x86.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0f82e2cbf64c..daa1918031df 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -702,7 +702,8 @@ static void kvm_load_guest_xcr0(struct kvm_vcpu *vcpu)
if (kvm_read_cr4_bits(vcpu, X86_CR4_OSXSAVE) &&
!vcpu->guest_xcr0_loaded) {
/* kvm_set_xcr() also depends on this */
- xsetbv(XCR_XFEATURE_ENABLED_MASK, vcpu->arch.xcr0);
+ if (vcpu->arch.xcr0 != host_xcr0)
+ xsetbv(XCR_XFEATURE_ENABLED_MASK, vcpu->arch.xcr0);
vcpu->guest_xcr0_loaded = 1;
}
}
Reviewed-by: Quan Xu <quan.xu0@xxxxxxxxx>