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@redhat.com>

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 5db50c1..5270711 100644 (file)
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -367,6 +367,10 @@ static int avic;
 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);