linux-kernel - Re: [RFC PATCH v5 083/104] KVM: x86: Split core of hypercall emulation to helper function

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Message-ID: <20220408053457.GA857847@ls.amr.corp.intel.com>
Date:   Thu, 7 Apr 2022 22:34:57 -0700
From:   Isaku Yamahata <isaku.yamahata@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sagi Shahar <sagis@...gle.com>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
        Jim Mattson <jmattson@...gle.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Connor Kuehl <ckuehl@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC PATCH v5 083/104] KVM: x86: Split core of hypercall
 emulation to helper function

On Thu, Apr 07, 2022 at 03:12:57PM +0200,
Paolo Bonzini <pbonzini@...hat.com> wrote:

> > > +       if (static_call(kvm_x86_get_cpl)(vcpu) != 0) {
> > > +               ret = -KVM_EPERM;
> > > +               goto out;
> > > +       }
> 
> Is this guaranteed by TDG.VP.VMCALL?

Yes. TDCALL instruction in TD results in #GP(0) if CPL > 0.
It's documented in trust domain CPU architectural extensions spec.
https://www.intel.com/content/dam/develop/external/us/en/documents-tps/intel-tdx-cpu-architectural-specification.pdf

Anyway VMM can't know TD guest CPL (or other CPU state).
-- 
Isaku Yamahata <isaku.yamahata@...il.com>