linux-kernel - Re: [PATCH 4/9] KVM: x86/mmu: Rename MMU_WARN_ON() to KVM_MMU_WARN

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Message-ID: <ZF7KbsCXBQHnOv7g@google.com>
Date:   Fri, 12 May 2023 16:23:26 -0700
From:   David Matlack <dmatlack@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Mingwei Zhang <mizhang@...gle.com>,
        Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH 4/9] KVM: x86/mmu: Rename MMU_WARN_ON() to
 KVM_MMU_WARN_ON()

On Thu, May 11, 2023 at 04:59:12PM -0700, Sean Christopherson wrote:
> Rename MMU_WARN_ON() to make it super obvious that the assertions are
> all about KVM's MMU, not the primary MMU.

I think adding KVM is a step in the right direction but I have 2
remaining problems with KVM_MMU_WARN_ON():

 - Reminds me of VM_WARN_ON(), which toggles between WARN_ON() and
   BUG_ON(), whereas KVM_MMU_WARN_ON() toggles between no-op and
   WARN_ON().

 - It's not obvious from the name that it's a no-op most of the time.

Naming is hard so I might just make things worse by trying but...

How about KVM_MMU_PROVE(condition). That directly pairs it with the new
CONFIG_KVM_PROVE_MMU(), makes it sufficiently different from
VM_WARN_ON() and WARN_ON() that readers will not make assumptions about
what's happening under the hood. Also "PROVE" sounds like a high bar
which conveys this might not always be enabled.

That also will allow us to convert this to a WARN_ON_ONCE() (my
suggestion on the other patch) without having to make the name any
longer.