2017-12-13 12:52:01

by Paolo Bonzini

Subject: [PATCH] KVM: x86: avoid unnecessary XSETBV on guest entry

xsetbv can be expensive when running on nested virtualization, try to
avoid it.

Signed-off-by: Paolo Bonzini <[email protected]>
---
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;
}
}
--
1.8.3.1

2017-12-13 19:03:36

by Jim Mattson

Subject: Re: [PATCH] KVM: x86: avoid unnecessary XSETBV on guest entry

Reviewed-by: Jim Mattson <[email protected]>

On Wed, Dec 13, 2017 at 4:51 AM, Paolo Bonzini <[email protected]> wrote:
> xsetbv can be expensive when running on nested virtualization, try to
> avoid it.
>
> Signed-off-by: Paolo Bonzini <[email protected]>
> ---
> 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;
> }
> }
> --
> 1.8.3.1
>

2017-12-14 01:05:36

by Wanpeng Li

Subject: Re: [PATCH] KVM: x86: avoid unnecessary XSETBV on guest entry

2017-12-13 20:51 GMT+08:00 Paolo Bonzini <[email protected]>:
> xsetbv can be expensive when running on nested virtualization, try to
> avoid it.
>
> Signed-off-by: Paolo Bonzini <[email protected]>

Reviewed-by: Wanpeng Li <[email protected]>

> ---
> 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;
> }
> }
> --
> 1.8.3.1
>

2017-12-14 03:27:34

by Quan Xu

Subject: Re: [PATCH] KVM: x86: avoid unnecessary XSETBV on guest entry

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 <[email protected]>
> ---
> 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 <[email protected]>