Commit 54b98bff authored Nov 10, 2014 by Andy Lutomirski Committed by Paolo Bonzini Nov 12, 2014

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>

parent f6577a5f

arch/x86/kvm/vmx.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -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;
		}

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