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From: Quan Xu <quan.xu0@gmail.com>
To: Paolo Bonzini <pbonzini@redhat.com>,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: wanpeng.li@hotmail.com
Subject: Re: [PATCH] KVM: x86: avoid unnecessary XSETBV on guest entry
Date: Thu, 14 Dec 2017 11:27:27 +0800	[thread overview]
Message-ID: <f22b5190-2beb-5b2a-02ec-dbad5f0a8a7d@gmail.com> (raw)
In-Reply-To: <1513169512-28139-1-git-send-email-pbonzini@redhat.com>



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@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;
>   	}
>   }

Reviewed-by: Quan Xu <quan.xu0@gmail.com>

      parent reply	other threads:[~2017-12-14  3:27 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
2017-12-14  1:05 ` Wanpeng Li
2017-12-14  3:27 ` Quan Xu [this message]

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