kvm: svm: Only propagate next_rip when guest supports it

Currently we always write the next_rip of the shadow vmcb to
the guests vmcb when we emulate a vmexit. This could confuse
the guest when its cpuid indicated no support for the
next_rip feature.

Fix this by only propagating next_rip if the guest actually
supports it.

Cc: Bandan Das <bsd@redhat.com>
Cc: Dirk Mueller <dmueller@suse.com>
Tested-By: Dirk Mueller <dmueller@suse.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

2 files changed, 31 insertions, 1 deletions

diff --git a/arch/x86/kvm/cpuid.h b/arch/x86/kvm/cpuid.h
index d434ee952b00..06332cb7e7d1 100644
--- a/arch/x86/kvm/cpuid.h
+++ b/arch/x86/kvm/cpuid.h
@@ -149,4 +149,25 @@ static inline bool guest_cpuid_has_rdtscp(struct kvm_vcpu *vcpu)
         best = kvm_find_cpuid_entry(vcpu, 0x80000001, 0);
         return best && (best->edx & bit(X86_FEATURE_RDTSCP));
 }
+
+/*
+ * NRIPS is provided through cpuidfn 0x8000000a.edx bit 3
+ */
+#define BIT_NRIPS       3
+
+static inline bool guest_cpuid_has_nrips(struct kvm_vcpu *vcpu)
+{
+        struct kvm_cpuid_entry2 *best;
+
+        best = kvm_find_cpuid_entry(vcpu, 0x8000000a, 0);
+
+        /*
+         * NRIPS is a scattered cpuid feature, so we can't use
+         * X86_FEATURE_NRIPS here (X86_FEATURE_NRIPS would be bit
+         * position 8, not 3).
+         */
+        return best && (best->edx & bit(BIT_NRIPS));
+}
+#undef BIT_NRIPS
+
 #endif
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 54a86183e5d3..cd8659cfc632 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -159,6 +159,9 @@ struct vcpu_svm {
         u32 apf_reason;
 
         u64  tsc_ratio;
+
+        /* cached guest cpuid flags for faster access */
+        bool nrips_enabled      : 1;
 };
 
 static DEFINE_PER_CPU(u64, current_tsc_ratio);
@@ -2365,7 +2368,9 @@ static int nested_svm_vmexit(struct vcpu_svm *svm)
         nested_vmcb->control.exit_info_2       = vmcb->control.exit_info_2;
         nested_vmcb->control.exit_int_info     = vmcb->control.exit_int_info;
         nested_vmcb->control.exit_int_info_err = vmcb->control.exit_int_info_err;
-        nested_vmcb->control.next_rip          = vmcb->control.next_rip;
+
+        if (svm->nrips_enabled)
+                nested_vmcb->control.next_rip  = vmcb->control.next_rip;
 
         /*
          * If we emulate a VMRUN/#VMEXIT in the same host #vmexit cycle we have
@@ -4085,6 +4090,10 @@ static u64 svm_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
 
 static void svm_cpuid_update(struct kvm_vcpu *vcpu)
 {
+        struct vcpu_svm *svm = to_svm(vcpu);
+
+        /* Update nrips enabled cache */
+        svm->nrips_enabled = !!guest_cpuid_has_nrips(&svm->vcpu);
 }
 
 static void svm_set_supported_cpuid(u32 func, struct kvm_cpuid_entry2 *entry)