Re: [PATCH 1/8] KVM: nSVM: Sync next_rip field from vmcb12 to vmcb02

Paolo Bonzini
2022-04-20T15:00:48Z

On 4/4/22 19:21, Sean Christopherson wrote:
> On Mon, Apr 04, 2022, Maciej S. Szmigiero wrote:
>>> @@ -1606,7 +1622,7 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
>>> nested_copy_vmcb_control_to_cache(svm, ctl);
>>> svm_switch_vmcb(svm, &svm->nested.vmcb02);
>>> - nested_vmcb02_prepare_control(svm);
>>> + nested_vmcb02_prepare_control(svm, save->rip);
>>
>> ^
>> I guess this should be "svm->vmcb->save.rip", since
>> KVM_{GET,SET}_NESTED_STATE "save" field contains vmcb01 data,
>> not vmcb{0,1}2 (in contrast to the "control" field).
>
> Argh, yes. Is userspace required to set L2 guest state prior to KVM_SET_NESTED_STATE?
> If not, this will result in garbage being loaded into vmcb02.
>

Let's just require X86_FEATURE_NRIPS, either in general or just to
enable nested virtualiazation, i.e.:

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index fc1725b7d05f..f8fc8a1b09f1 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4904,10 +4904,12 @@ static __init int svm_hardware_setup(void)
goto err;
}

- if (nrips) {
- if (!boot_cpu_has(X86_FEATURE_NRIPS))
- nrips = false;
- }
+ if (!boot_cpu_has(X86_FEATURE_NRIPS))
+ nrips = false;
+ if (nested & !nrips) {
+ pr_warn("Next RIP Save not available, disabling nested virtualization\n");
+ nested = false;
+ }

enable_apicv = avic = avic && npt_enabled && (boot_cpu_has(X86_FEATURE_AVIC) || force_avic);

If I looked it up correctly it was introduced around 2010-2011.

Paolo