From: Paolo Bonzini <pbonzini@redhat.com>
Date: Wed, 13 Dec 2017 12:51:32 +0000 (+0100)
Subject: KVM: x86: avoid unnecessary XSETBV on guest entry
X-Git-Tag: v4.16-rc1~10^2~39
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=476b7adaa3272557168b287175b1e9e943913404;p=thirdparty%2Flinux.git

KVM: x86: avoid unnecessary XSETBV on guest entry

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

Reviewed-by: Jim Mattson <jmattson@google.com>
Reviewed-by: Wanpeng Li <wanpeng.li@hotmail.com>
Reviewed-by: Quan Xu <quan.xu0@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
---

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a3dd44bb6f1e6..56d8a1e11e50b 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;
 	}
 }