linux-kernel - Re: [PATCH] Add KVM_EXIT_SHUTDOWN metadata for SEV-ES

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Message-ID: <CAMkAt6qB8GXhu0h+k1pbP_KkhvW+Edk-=zyo3zo2WdOe_qq8PA@mail.gmail.com>
Date:   Fri, 25 Mar 2022 09:28:47 -0600
From:   Peter Gonda <pgonda@...gle.com>
To:     Marc Orr <marcorr@...gle.com>
Cc:     kvm list <kvm@...r.kernel.org>, Borislav Petkov <bp@...en8.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        Brijesh Singh <brijesh.singh@....com>,
        Joerg Roedel <jroedel@...e.de>,
        Sean Christopherson <seanjc@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Add KVM_EXIT_SHUTDOWN metadata for SEV-ES

On Mon, Mar 21, 2022 at 1:45 PM Marc Orr <marcorr@...gle.com> wrote:
>
> On Mon, Mar 21, 2022 at 11:08 AM Peter Gonda <pgonda@...gle.com> wrote:
> >
> > > > diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> > > > index 75fa6dd268f0..5f9d37dd3f6f 100644
> > > > --- a/arch/x86/kvm/svm/sev.c
> > > > +++ b/arch/x86/kvm/svm/sev.c
> > > > @@ -2735,8 +2735,13 @@ static int sev_handle_vmgexit_msr_protocol(struct vcpu_svm *svm)
> > > >                 pr_info("SEV-ES guest requested termination: %#llx:%#llx\n",
> > > >                         reason_set, reason_code);
> > > >
> > > > -               ret = -EINVAL;
> > > > -               break;
> > > > +               vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN;
> > > > +               vcpu->run->shutdown.reason = KVM_SHUTDOWN_SEV_TERM;
> > > > +               vcpu->run->shutdown.ndata = 2;
> > > > +               vcpu->run->shutdown.data[0] = reason_set;
> > > > +               vcpu->run->shutdown.data[1] = reason_code;
> > > > +
> > > > +               return 0;
> > >
> > > Maybe I'm missing something, but don't we want to keep returning an error?
> > >
> > > rationale: Current behavior: return -EINVAL to userpsace, but
> > > userpsace cannot infer where the -EINVAL came from. After this patch:
> > > We should still return -EINVAL to userspace, but now userspace can
> > > parse this new info in the KVM run struct to properly terminate.
> > >
> >
> > I removed the error return code here since an SEV guest may request a
> > termination due to no fault of the host at all. This is now inline
> > with any other shutdown requested by the guest. I don't have a strong
> > preference here but EINVAL doesn't seem correct in all cases, do
> > others have any thoughts on this?
>
> Makes sense. Yeah, let's see if others have an opinion. Otherwise, I'm
> fine either way. Now that you mention it, returning an error to
> userspace when the guest triggered the self-termination, and could've
> done so for reasons outside the host's control, is a little odd. But
> at the same time, it's just as likely that the guest is
> self-terminating due to a host-side error. So I guess it's not clear
> whether returning an error here is "right" or "wrong".

Since no one has expressed a strong opinion have have left this part
of the patch unchanged in the V2. Happy to revise again if people
prefer something else.