[v2,05/18] KVM: vmx: do not unconditionally clear EFER switching
diff mbox series

Message ID 20180828160459.14093-6-sean.j.christopherson@intel.com
State New
Headers show
Series
  • KVM: nVMX: add option to perform early consistency checks via H/W
Related show

Commit Message

Sean Christopherson Aug. 28, 2018, 4:04 p.m. UTC
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: Sean Christopherson <sean.j.christopherson@intel.com>
---
 arch/x86/kvm/vmx.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Comments

Jim Mattson Sept. 19, 2018, 9:29 p.m. UTC | #1
On Tue, Aug 28, 2018 at 9:04 AM, Sean Christopherson
<sean.j.christopherson@intel.com> wrote:
> 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: Sean Christopherson <sean.j.christopherson@intel.com>

Reviewed-by: Jim Mattson <jmattson@google.com>

Patch
diff mbox series

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 6097d0115056..1fcf374a1475 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2798,8 +2798,6 @@  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
@@ -2812,8 +2810,12 @@  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;