[PATCH 3.10 21/22] KVM: nSVM: Check for NRIPS support before updating control field

Greg Kroah-Hartman
2015-07-01T18:53:22Z

From: Bandan Das <bsd@redhat.com>

commit f104765b4f81fd74d69e0eb161e89096deade2db upstream.

If hardware doesn't support DecodeAssist - a feature that provides
more information about the intercept in the VMCB, KVM decodes the
instruction and then updates the next_rip vmcb control field.
However, NRIP support itself depends on cpuid Fn8000_000A_EDX[NRIPS].
Since skip_emulated_instruction() doesn't verify nrip support
before accepting control.next_rip as valid, avoid writing this
field if support isn't present.

Signed-off-by: Bandan Das <bsd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/kvm/svm.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -495,8 +495,10 @@ static void skip_emulated_instruction(st
{
struct vcpu_svm *svm = to_svm(vcpu);

- if (svm->vmcb->control.next_rip != 0)
+ if (svm->vmcb->control.next_rip != 0) {
+ WARN_ON(!static_cpu_has(X86_FEATURE_NRIPS));
svm->next_rip = svm->vmcb->control.next_rip;
+ }

if (!svm->next_rip) {
if (emulate_instruction(vcpu, EMULTYPE_SKIP) !=
@@ -4229,7 +4231,9 @@ static int svm_check_intercept(struct kv
break;
}

- vmcb->control.next_rip = info->next_rip;
+ /* TODO: Advertise NRIPS to guest hypervisor unconditionally */
+ if (static_cpu_has(X86_FEATURE_NRIPS))
+ vmcb->control.next_rip = info->next_rip;
vmcb->control.exit_code = icpt_info.exit_code;
vmexit = nested_svm_exit_handled(svm);