linux-kernel - Re: [RFC PATCH 13/18] KVM: x86/mmu: Adjust SPTE_MMIO_ALLOWED

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Message-ID: <aCJN789_iZa6omeu@google.com>
Date: Mon, 12 May 2025 12:37:19 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Jon Kohler <jon@...anix.com>
Cc: pbonzini@...hat.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, 
	dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com, 
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 13/18] KVM: x86/mmu: Adjust SPTE_MMIO_ALLOWED_MASK to
 understand MBEC

Please be more precise with the shortlogs.  "Understand MBEC" is extremely vague.

On Thu, Mar 13, 2025, Jon Kohler wrote:
> Adjust the SPTE_MMIO_ALLOWED_MASK and associated values to make these
> masks aware of PTE Bit 10, to be used by Intel MBEC.

Same thing here.  "aware of PTE bit 10" doesn't describe the change in a way that
allows for quick review of the patch.  E.g. 

  KVM: x86/mmu: Exclude EPT MBEC's user-executable bit from the MMIO generation

The changelogs also need to explain *why*.  If you actually tried to write out
justification for why KVM can't use bit 10 for the MMIO generation, then unless
you start making stuff up (or Chao and I are missing something), you'll come to
same conclusion that Chao and I came to: this patch is unnecessary.