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Commit 02343cf2 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
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KVM: vmx: do not unconditionally clear EFER switching 



Do not unconditionally call clear_atomic_switch_msr() when updating
EFER.  This adds up to four unnecessary VMWrites in the case where
guest_efer != host_efer, e.g. if the load_on_{entry,exit} bits were
already set.

Signed-off-by: default avatarSean Christopherson <sean.j.christopherson@intel.com>
Reviewed-by: default avatarJim Mattson <jmattson@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent b7031fd4

arch/x86/kvm/vmx.c

+4 −2
Original line number Diff line number Diff line
@@ -2790,8 +2790,6 @@ static bool update_transition_efer(struct vcpu_vmx *vmx, int efer_offset) 
		ignore_bits &= ~(u64)EFER_SCE;

#endif



	clear_atomic_switch_msr(vmx, MSR_EFER);



	/*

	 * On EPT, we can't emulate NX, so we must switch EFER atomically.

	 * On CPUs that support "load IA32_EFER", always switch EFER
@@ -2804,8 +2802,12 @@ static bool update_transition_efer(struct vcpu_vmx *vmx, int efer_offset) 
		if (guest_efer != host_efer)

			add_atomic_switch_msr(vmx, MSR_EFER,

					      guest_efer, host_efer, false);

		else

			clear_atomic_switch_msr(vmx, MSR_EFER);

		return false;

	} else {

		clear_atomic_switch_msr(vmx, MSR_EFER);



		guest_efer &= ~ignore_bits;

		guest_efer |= host_efer & ignore_bits;