KVM: vmx, svm: always run with EFER.NXE=1 when shadow paging is active

VMX already does so if the host has SMEP, in order to support the combination of CR0.WP=1 and CR4.SMEP=1. However, it is perfectly safe to always do so, and in fact VMX already ends up running with EFER.NXE=1 on old processors that lack the "load EFER" controls, because it may help avoiding a slow MSR write. Removing all the conditionals simplifies the code. SVM does not have similar code, but it should since recent AMD processors do support SMEP. So this patch also makes the code for the two vendors more similar while fixing NPT=0, CR0.WP=1 and CR4.SMEP=1 on AMD processors. Cc: [email protected] Cc: Joerg Roedel <[email protected]> Signed-off-by: Paolo Bonzini <[email protected]>
RufUsul · Oct 31, 2019 · 9167ab7 · 9167ab7
1 parent a97b0e7
commit 9167ab7
Show file tree

Hide file tree

Showing 2 changed files with 11 additions and 13 deletions.
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
@@ -734,8 +734,14 @@ static int get_npt_level(struct kvm_vcpu *vcpu)
 static void svm_set_efer(struct kvm_vcpu *vcpu, u64 efer)
 {
 	vcpu->arch.efer = efer;
-	if (!npt_enabled && !(efer & EFER_LMA))
-		efer &= ~EFER_LME;
+
+	if (!npt_enabled) {
+		/* Shadow paging assumes NX to be available.  */
+		efer |= EFER_NX;
+
+		if (!(efer & EFER_LMA))
+			efer &= ~EFER_LME;
+	}
 
 	to_svm(vcpu)->vmcb->save.efer = efer | EFER_SVME;
 	mark_dirty(to_svm(vcpu)->vmcb, VMCB_CR);

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
@@ -969,17 +969,9 @@ static bool update_transition_efer(struct vcpu_vmx *vmx, int efer_offset)
 	u64 guest_efer = vmx->vcpu.arch.efer;
 	u64 ignore_bits = 0;
 
-	if (!enable_ept) {
-		/*
-		 * NX is needed to handle CR0.WP=1, CR4.SMEP=1.  Testing
-		 * host CPUID is more efficient than testing guest CPUID
-		 * or CR4.  Host SMEP is anyway a requirement for guest SMEP.
-		 */
-		if (boot_cpu_has(X86_FEATURE_SMEP))
-			guest_efer |= EFER_NX;
-		else if (!(guest_efer & EFER_NX))
-			ignore_bits |= EFER_NX;
-	}
+	/* Shadow paging assumes NX to be available.  */
+	if (!enable_ept)
+		guest_efer |= EFER_NX;
 
 	/*
 	 * LMA and LME handled by hardware; SCE meaningless outside long mode.