linux-kernel - [PATCH] KVM: svm: add nrips module parameter

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Message-Id: <1561032813-16698-1-git-send-email-pbonzini@redhat.com>
Date:   Thu, 20 Jun 2019 14:13:33 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: [PATCH] KVM: svm: add nrips module parameter

Allow testing code for old processors that lack the next RIP save
feature, by disabling usage of the next_rip field.

Nested hypervisors however get the feature unconditionally.

Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
 arch/x86/kvm/svm.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 735b8c01895e..fe046c13f03b 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -367,6 +367,10 @@ struct amd_svm_iommu_ir {
 module_param(avic, int, S_IRUGO);
 #endif
 
+/* enable/disable Next RIP Save */
+static int nrips = true;
+module_param(nrips, int, 0444);
+
 /* enable/disable Virtual VMLOAD VMSAVE */
 static int vls = true;
 module_param(vls, int, 0444);
@@ -773,7 +777,7 @@ static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_svm *svm = to_svm(vcpu);
 
-	if (svm->vmcb->control.next_rip != 0) {
+	if (nrips && svm->vmcb->control.next_rip != 0) {
 		WARN_ON_ONCE(!static_cpu_has(X86_FEATURE_NRIPS));
 		svm->next_rip = svm->vmcb->control.next_rip;
 	}
@@ -810,7 +814,7 @@ static void svm_queue_exception(struct kvm_vcpu *vcpu)
 
 	kvm_deliver_exception_payload(&svm->vcpu);
 
-	if (nr == BP_VECTOR && !static_cpu_has(X86_FEATURE_NRIPS)) {
+	if (nr == BP_VECTOR && !nrips) {
 		unsigned long rip, old_rip = kvm_rip_read(&svm->vcpu);
 
 		/*
@@ -1367,6 +1371,11 @@ static __init int svm_hardware_setup(void)
 	} else
 		kvm_disable_tdp();
 
+	if (nrips) {
+		if (!boot_cpu_has(X86_FEATURE_NRIPS))
+			nrips = false;
+	}
+
 	if (avic) {
 		if (!npt_enabled ||
 		    !boot_cpu_has(X86_FEATURE_AVIC) ||
@@ -3938,7 +3947,7 @@ static int rdpmc_interception(struct vcpu_svm *svm)
 {
 	int err;
 
-	if (!static_cpu_has(X86_FEATURE_NRIPS))
+	if (!nrips)
 		return emulate_on_interception(svm);
 
 	err = kvm_rdpmc(&svm->vcpu);
-- 
1.8.3.1