linux-kernel - Re: [PATCH v5 2/2] kvm: nVMX: Introduce KVM_CAP_NESTED

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Date:   Wed, 18 Jul 2018 11:03:55 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     Radim Krčmář <rkrcmar@...hat.com>
Cc:     KarimAllah Ahmed <karahmed@...zon.de>,
        LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: [PATCH v5 2/2] kvm: nVMX: Introduce KVM_CAP_NESTED_STATE

On Wed, Jul 18, 2018 at 10:55 AM, Radim Krčmář <rkrcmar@...hat.com> wrote:

>> +     vmx->nested.nested_run_pending = 1;
>
> This is not necessary.  We're only copying state and do not add anything
> that would be lost on a nested VM exit without prior VM entry.

If nested_run_pending is blindly set on restore, then prepare_vmcs02
will do the wrong thing. For example, if there was an injected event
in the vmcs12, it will get injected again, even if the vCPU has been
in L2 for some time.

The value of nested_run_pending should always come from the saved VMX
state (a few lines above).