linux-kernel - Re: [V4 PATCH 4/4] KVM: selftests: x86: Invoke kvm hypercall as per host cpu

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Message-ID: <CAGtprH_F-U799DT9OkrC=pEQJYt0=Tj2WWuKuczm6z2ftUZuQA@mail.gmail.com>
Date:   Tue, 10 Jan 2023 16:18:15 -0800
From:   Vishal Annapurve <vannapurve@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, pbonzini@...hat.com,
        shuah@...nel.org, bgardon@...gle.com, oupton@...gle.com,
        peterx@...hat.com, vkuznets@...hat.com, dmatlack@...gle.com
Subject: Re: [V4 PATCH 4/4] KVM: selftests: x86: Invoke kvm hypercall as per
 host cpu

On Mon, Jan 9, 2023 at 10:21 AM Sean Christopherson <seanjc@...gle.com> wrote:
>
> KVM: selftests: Use host's native hypercall instruction in kvm_hypercall()
>
> On Wed, Dec 28, 2022, Vishal Annapurve wrote:
> > Invoke vmcall/vmmcall instructions from kvm_hypercall as per host CPU
>
> () for functions, i.e. kvm_hypercall().
>
> > type.
>
> s/type/vendor, "type" is too generic.
>
> > CVMs and current kvm_hyerpcall callers need to execute hypercall
>
> CVM isn't a not ubiquitous acronym.  I would avoid it entirely because "CVM"
> doesn't strictly imply memory encryption, e.g. KVM could still patch the guest in
> a pKVM-like implementation.
>
>   Use the host CPU's native hypercall instruction, i.e. VMCALL vs. VMMCALL,
>   in kvm_hypercall(), as relying on KVM to patch in the native hypercall on
>   a #UD for the "wrong" hypercall requires KVM_X86_QUIRK_FIX_HYPERCALL_INSN
>   to be enabled and flat out doesn't work if guest memory is encrypted with
>   a private key, e.g. for SEV VMs.

Ack, this makes sense.