linux-kernel - Re: [PATCH v2 2/4] KVM: nSVM: correctly restore nested_run

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Date:   Thu, 7 Jan 2021 22:05:29 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>,
        Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH v2 2/4] KVM: nSVM: correctly restore nested_run_pending on
 migration

On 07/01/21 21:19, Sean Christopherson wrote:
>> That said, the v1 change had some appeal to it.
> 
> Which v1 change are you referring to?

Moving the to-be-injected event from eventinj to vcpu->arch, and from 
there to vmcb02 on the next vmentry's inject_pending_event.

>> In the VMX case (if properly implemented) it would allow removing the weird
>> nested_run_pending case from prepare_vmcs02_early.  I think it's a valuable
>> invariant that there are no events in the VMCS after each KVM_RUN iteration,
>> and this special case is breaking the invariant.
>
> Hmm, as weird as that code is, I think it's actually the most architecturally
> correct behavior.

I was referring to the "then" branch therein. :)

Paolo