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Commit 54b98bff authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Paolo Bonzini
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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: default avatarAndy 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: default avatarPaolo 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;

	}