2015-06-11 06:05:43

by Bandan Das

Subject: [PATCH] KVM: nSVM: Check for NRIPS support before updating control field

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 <[email protected]>
---
arch/x86/kvm/svm.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 9afa233..4911bf1 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -511,8 +511,10 @@ static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
{
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) !=
@@ -4317,7 +4319,9 @@ static int svm_check_intercept(struct kvm_vcpu *vcpu,
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);

--
2.1.0

2015-06-17 12:31:37

by Paolo Bonzini

Subject: Re: [PATCH] KVM: nSVM: Check for NRIPS support before updating control field

On 11/06/2015 08:05, Bandan Das wrote:
>
> 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 <[email protected]>
> ---
> arch/x86/kvm/svm.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 9afa233..4911bf1 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -511,8 +511,10 @@ static void skip_emulated_instruction(struct kvm_vcpu *vcpu)
> {
> 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) !=
> @@ -4317,7 +4319,9 @@ static int svm_check_intercept(struct kvm_vcpu *vcpu,
> 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);
>
>

Applied, thanks.

paolo