From: Paolo Bonzini <pbonzini@redhat.com>
To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Cc: wanpeng.li@hotmail.com
Subject: [PATCH] KVM: x86: avoid unnecessary XSETBV on guest entry
Date: Wed, 13 Dec 2017 13:51:52 +0100 [thread overview]
Message-ID: <1513169512-28139-1-git-send-email-pbonzini@redhat.com> (raw)
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
next reply other threads:[~2017-12-13 12:52 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-13 12:51 Paolo Bonzini [this message]
2017-12-13 19:03 ` Jim Mattson
2017-12-14 1:05 ` Wanpeng Li
2017-12-14 3:27 ` Quan Xu
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