Re: [PATCH 2/4] KVM: x86/tdp_mmu: Merge the prefetch into the is_access_allowed() check

[Sean Christopherson]

On Fri, Feb 07, 2025, Yan Zhao wrote:
> Merge the prefetch check into the is_access_allowed() check to determine a
> spurious fault.
> 
> In the TDP MMU, a spurious prefetch fault should also pass the
> is_access_allowed() check.

How so? 

  1. vCPU takes a write-fault on a swapped out page and queues an async #PF
  2. A different task installs a writable SPTE
  3. A third task write-protects the SPTE for dirty logging
  4. Async #PF handler faults in the SPTE, encounters a read-only SPTE for its
     write fault.

KVM shouldn't mark the gfn as dirty in this case.