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

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Message-ID: <Y7xbC+leVdO0TRVE@google.com>
Date:   Mon, 9 Jan 2023 18:20:59 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Vishal Annapurve <vannapurve@...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

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.