linux-kernel - Re: [PATCH 2/2] KVM: SVM: Raise #UD if VMMCALL instruction is not intercepted

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Message-ID: <29ea5ead-1ee3-4ecd-ad4a-63fd99a7f67f@citrix.com>
Date: Tue, 6 Jan 2026 20:40:27 +0000
From: Andrew Cooper <andrew.cooper3@...rix.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Andrew Cooper <andrew.cooper3@...rix.com>, chengkev@...gle.com,
 kvm@...r.kernel.org, linux-kernel@...r.kernel.org, pbonzini@...hat.com,
 yosry.ahmed@...ux.dev
Subject: Re: [PATCH 2/2] KVM: SVM: Raise #UD if VMMCALL instruction is not
 intercepted

On 06/01/2026 6:57 pm, Sean Christopherson wrote:
> On Tue, Jan 06, 2026, Andrew Cooper wrote:
>>> Mentioning L2 and L1 is confusing.  It reads like arbitrary KVM behavior.  And
>>> IMO the most notable thing is what's missing: an intercept check.  _That_ is
>>> worth commenting, e.g.
>>>
>>> 	/*
>>> 	 * VMMCALL #UDs if it's not intercepted, and KVM reaches this point if
>>> 	 * and only if the VMCALL intercept is not set in vmcb12.
>>> 	 */
>> Not intercepting VMMCALL is stated to be an unconditional VMRUN
>> failure.  APM Vol3 15.5 Canonicalization and Consistency Checks.
> Hrm, I can't find that.  I see:
>
>   The VMRUN intercept bit is clear.
>
> but I don't see anything about VMMCALL being a mandatory intercept.

Gah.  I even double checked before sending, but I'm apparently
completely blind to the difference between VMRUN and VMMCALL.

Sorry for the noise.

~Andrew