From: Sean Christopherson <seanjc@google.com>
To: Ashish Kalra <ashish.kalra@amd.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
srutherford@google.com, joro@8bytes.org, brijesh.singh@amd.com,
thomas.lendacky@amd.com, venu.busireddy@oracle.com,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Borislav Petkov <bp@suse.de>,
x86@kernel.org
Subject: Re: [PATCH 0/3] KVM: x86: guest interface for SEV live migration
Date: Tue, 20 Apr 2021 18:58:14 +0000 [thread overview]
Message-ID: <YH8kRs8KGmLaJ6EN@google.com> (raw)
In-Reply-To: <YH8gKcxE+dfulftQ@google.com>
On Tue, Apr 20, 2021, Sean Christopherson wrote:
> On Tue, Apr 20, 2021, Ashish Kalra wrote:
> > On Tue, Apr 20, 2021 at 05:31:07PM +0000, Sean Christopherson wrote:
> > > On Tue, Apr 20, 2021, Paolo Bonzini wrote:
> > > > + case KVM_HC_PAGE_ENC_STATUS: {
> > > > + u64 gpa = a0, npages = a1, enc = a2;
> > > > +
> > > > + ret = -KVM_ENOSYS;
> > > > + if (!vcpu->kvm->arch.hypercall_exit_enabled)
> > >
> > > I don't follow, why does the hypercall need to be gated by a capability? What
> > > would break if this were changed to?
> > >
> > > if (!guest_pv_has(vcpu, KVM_FEATURE_HC_PAGE_ENC_STATUS))
> > >
> >
> > But, the above indicates host support for page_enc_status_hc, so we want
> > to ensure that host supports and has enabled support for the hypercall
> > exit, i.e., hypercall has been enabled.
>
> I still don't see how parroting back KVM_GET_SUPPORTED_CPUID, i.e. "unintentionally"
> setting KVM_FEATURE_HC_PAGE_ENC_STATUS, would break anything. Sure, the guest
> does unnecessary hypercalls, but they're eaten by KVM. On the flip side, gating
> the hypercall on the capability, and especially only the capability, creates
> weird scenarios where the guest can observe KVM_FEATURE_HC_PAGE_ENC_STATUS=1
> but fail the hypercall. Those would be fairly clearcut VMM bugs, but at the
> same time KVM is essentially going out of its way to manufacture the problem.
Doh, I was thinking of the MSR behavior, not the hypercall. I'll respond to
Paolo's mail, I have one more hail mary idea.
next prev parent reply other threads:[~2021-04-20 18:58 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-20 11:20 [PATCH 0/3] KVM: x86: guest interface for SEV live migration Paolo Bonzini
2021-04-20 15:15 ` Sean Christopherson
2021-04-20 18:27 ` Paolo Bonzini
2021-04-20 17:31 ` Sean Christopherson
2021-04-20 18:11 ` Ashish Kalra
2021-04-20 18:40 ` Sean Christopherson
2021-04-20 18:58 ` Sean Christopherson [this message]
2021-04-20 18:39 ` Paolo Bonzini
2021-04-20 19:02 ` Sean Christopherson
2021-04-20 20:16 ` Sean Christopherson
2021-04-20 20:58 ` Paolo Bonzini
2021-04-20 22:49 ` Sean Christopherson
2021-04-20 23:20 ` Sean Christopherson
2021-04-21 12:03 ` Paolo Bonzini
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