Re: [PATCH] KVM: x86/mmu: Embed direct bits into gpa for KVM_PRE_FAULT_MEMORY

[Yan Zhao]

On Fri, Jun 13, 2025 at 02:50:48AM +0800, Edgecombe, Rick P wrote:
> On Thu, 2025-06-12 at 15:19 +0800, Yan Zhao wrote:
> > > TDX isn't setting PFERR_WRITE_MASK or PFERR_PRESENT_MASK in the error_code
> > > passed into the fault handler. So page_fault_can_be_fast() should return
> > > false
> > > for that reason for private/mirror faults.
> > Hmm, TDX does set PFERR_WRITE_MASK in the error_code when fault->prefetch is
> > false (since exit_qual is set to EPT_VIOLATION_ACC_WRITE in
> > tdx_handle_ept_violation()).
> > 
> > PFERR_PRESENT_MASK is always unset.
> > 
> > page_fault_can_be_fast() does always return false for private mirror faults
> > though, due to the reason in
> > https://lore.kernel.org/kvm/aEp6pDQgbjsfrg2h@xxxxxxxxxxxxxxxxxxxxxxxxx :)
> 
> Seems cleanup worthy to me, but not a bug. I think we should follow up,
> depending on the scope of Sean's cleanup.
Ok. There was an explicit disallowing of fast page fault for mirror [1].
Maybe we can add it back after Sean's cleanup.

[1] https://lore.kernel.org/kvm/af70ce8626cb7366d9b86a41c5d731f8ebd144ff.1708933498.git.isaku.yamahata@xxxxxxxxx/