linux-kernel - Re: [PATCH 1/8] KVM: nSVM: Sync next

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Message-ID: <98fca5c8-ca8e-be1f-857d-3d04041b66d7@maciej.szmigiero.name>
Date:   Wed, 20 Apr 2022 17:05:41 +0200
From:   "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [PATCH 1/8] KVM: nSVM: Sync next_rip field from vmcb12 to vmcb02

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