[PATCH v3 8/8] KVM: x86: Read CR4.DE in emulator if and only if accessing DR4 or DR5

[Sean Christopherson]

Micro-optimize emulation of MOV DR instructions by checking CR4.DE if and
only if DR4 or DR5 is being accessed.

No functional change intended.

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/kvm/emulate.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index e030ef9b9744..8071b372d233 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -3840,13 +3840,11 @@ static int check_dr_read(struct x86_emulate_ctxt *ctxt)
 {
 	bool is_intel = ctxt->ops->guest_cpuid_is_intel_compatible(ctxt);
 	int dr = ctxt->modrm_reg;
-	u64 cr4;
 
 	if (dr > 7)
 		return emulate_ud(ctxt);
 
-	cr4 = ctxt->ops->get_cr(ctxt, 4);
-	if ((cr4 & X86_CR4_DE) && (dr == 4 || dr == 5))
+	if ((dr == 4 || dr == 5) && (ctxt->ops->get_cr(ctxt, 4) & X86_CR4_DE))
 		return emulate_ud(ctxt);
 
 	/* Intel CPUs prioritize the DR7.GD=1 #DB over the CPL>0 #GP. */
-- 
2.54.0.1136.gdb2ca164c4-goog