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 a3dd44b..56d8a1e 100644 (file)
--- 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;
        }
 }