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

From: "Maciej S. Szmigiero" <mail@maciej.szmigiero.name>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	Sean Christopherson <seanjc@google.com>
Subject: Re: [PATCH 1/8] KVM: nSVM: Sync next_rip field from vmcb12 to vmcb02
Date: Wed, 20 Apr 2022 17:05:41 +0200	[thread overview]
Message-ID: <98fca5c8-ca8e-be1f-857d-3d04041b66d7@maciej.szmigiero.name> (raw)
In-Reply-To: <4505b43d-5c33-4199-1259-6d4e8ebac1ec@redhat.com>

On 20.04.2022 17:00, Paolo Bonzini wrote:
> 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

👍

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

A quick Internet search showed that the first CPUs with NextRIP were
the second-generation Family 10h CPUs (Phenom II, Athlon II, etc.).
They started being released in early 2009.

> Paolo

Thanks,
Maciej