Re: [PATCH] KVM: x86/mmu: Only zap valid non-mirror roots in kvm_zap_gfn_range()

[Yan Zhao <yan.y.zhao@intel.com>]

On Sun, Dec 22, 2024 at 08:28:56PM +0100, Paolo Bonzini wrote:
> On Fri, Nov 15, 2024 at 9:50 AM Yan Zhao <yan.y.zhao@intel.com> wrote:
> > Sean also suggested making the self-snoop feature a hard dependency for
> > enabling TDX [2].
> >
> > That is because
> > - TDX shared EPT is able to reuse the memory type specified in VMX's code
> >   as long as guest MTRRs are not referenced.
> > - KVM does not call kvm_zap_gfn_range() when attaching/detaching
> >   non-coherent DMA devices when the CPU have feature self-snoop. [3]
> >
> > However, [3] cannot be guaranteed after commit 9d70f3fec144 ("Revert "KVM:
> > VMX: Always honor guest PAT on CPUs that support self-snoop"), which was
> > due to a regression with the bochsdrm driver.
> 
> I think we should treat honoring of guest PAT like zap-memslot-only,
> and make it a quirk that TDX disables. Making it a quirk adds a bit of
> complexity, but it documents why the code exists and it makes it easy
> for TDX to disable it.
Thanks! Will do in this way after the new year.