linux-kernel - Re: [PATCH 3/4] KVM: x86/mmu: Make sure pfn is not changed for spurious fault

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Message-ID: <Z6Yhmg2nmUAtp4yn@google.com>
Date: Fri, 7 Feb 2025 07:07:06 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Yan Zhao <yan.y.zhao@...el.com>
Cc: pbonzini@...hat.com, rick.p.edgecombe@...el.com, 
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH 3/4] KVM: x86/mmu: Make sure pfn is not changed for
 spurious fault

On Fri, Feb 07, 2025, Yan Zhao wrote:
> Make sure pfn is not changed for a spurious fault by warning in the TDP
> MMU. For shadow path, only treat a prefetch fault as spurious when pfn is
> not changed, since the rmap removal and add are required when pfn is
> changed.

I like sanity checks, but I don't like special casing "prefetch" faults like this.
KVM should _never_ change the PFN of a shadow-present SPTE.  The TDP MMU already
BUG()s on this, and mmu_spte_update() WARNs on the transition.