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From: Jim Mattson <jmattson@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
	kvm list <kvm@vger.kernel.org>,
	Wanpeng Li <wanpeng.li@hotmail.com>
Subject: Re: [PATCH] KVM: x86: avoid unnecessary XSETBV on guest entry
Date: Wed, 13 Dec 2017 11:03:31 -0800	[thread overview]
Message-ID: <CALMp9eScSH1qVczw38NxAA7UAXcNTVT6WWVUuAe=WbNGTfCe3w@mail.gmail.com> (raw)
In-Reply-To: <1513169512-28139-1-git-send-email-pbonzini@redhat.com>

Reviewed-by: Jim Mattson <jmattson@google.com>

On Wed, Dec 13, 2017 at 4:51 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> xsetbv can be expensive when running on nested virtualization, try to
> avoid it.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  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
>

  reply	other threads:[~2017-12-13 19:03 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-12-13 12:51 [PATCH] KVM: x86: avoid unnecessary XSETBV on guest entry Paolo Bonzini
2017-12-13 19:03 ` Jim Mattson [this message]
2017-12-14  1:05 ` Wanpeng Li
2017-12-14  3:27 ` Quan Xu

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