summaryrefslogtreecommitdiff
diff options
context:
space:
mode:
authorAndy Lutomirski <luto@amacapital.net>2014-11-10 11:19:15 -0800
committerPaolo Bonzini <pbonzini@redhat.com>2014-11-12 16:27:21 +0100
commit54b98bff8ef4ccfc6f638c5ed868d2d51cdde585 (patch)
tree277011bfa483c42e0f04605f2859eb6cc9142cae
parentf6577a5fa15d82217ca73c74cd2dcbc0f6c781dd (diff)
x86, kvm, vmx: Don't set LOAD_IA32_EFER when host and guest match
There's nothing to switch if the host and guest values are the same. I am unable to find evidence that this makes any difference whatsoever. Signed-off-by: Andy Lutomirski <luto@amacapital.net> [I could see a difference on Nehalem. From 5 runs: userspace exit, guest!=host 12200 11772 12130 12164 12327 userspace exit, guest=host 11983 11780 11920 11919 12040 lightweight exit, guest!=host 3214 3220 3238 3218 3337 lightweight exit, guest=host 3178 3193 3193 3187 3220 This passes the t-test with 99% confidence for userspace exit, 98.5% confidence for lightweight exit. - Paolo] Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
-rw-r--r--arch/x86/kvm/vmx.c4
1 files changed, 3 insertions, 1 deletions
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 0d25fc16d98b..330a08aa0291 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -1673,7 +1673,9 @@ static bool update_transition_efer(struct vcpu_vmx *vmx, int efer_offset)
guest_efer = vmx->vcpu.arch.efer;
if (!(guest_efer & EFER_LMA))
guest_efer &= ~EFER_LME;
- add_atomic_switch_msr(vmx, MSR_EFER, guest_efer, host_efer);
+ if (guest_efer != host_efer)
+ add_atomic_switch_msr(vmx, MSR_EFER,
+ guest_efer, host_efer);
return false;
}