Re: [PATCH v10 047/108] KVM: x86/tdp_mmu: Don't zap private pages for unsupported cases

Huang, Kai
2022-12-15T23:06:37Z

On Thu, 2022-12-15 at 14:46 -0800, Isaku Yamahata wrote:
> > Btw, as you mentioned in the changelog, private memory always has WB memory
> > type, thus cannot be virtualized.  Is it better to modify update_mtrr() to
> > just
> > return early if the gfn range is purely private?
>
> MTRR support in cpuid is fixed to 1, PAT in cpuid is native.
> MTRR and PAT are supported on shared pages.
>

But none of those are mentioned in the changelog or whatever. They are hidden
in the spec or in the later patches far away.

ALso, the handling of "load/save IA32_PAT" in VMEXIT/VMENTRY VMCS control is
different between TDX module and KVM. None of those are mentioned.

All those make the patch review so hard.

>
> > IMHO the handling of MTRR/PAT virtualization for TDX guest deserves
> > dedicated
> > patch(es) to put them together so it's easier to review.  Now the relevant
> > parts
> > spread in multiple independent patches (MSR handling, vt_get_mt_mask(),
> > etc).
>
> Ok, let me check it.

Yes. IMHO you should put all relevant parts together and make a clear changelog
to justify the patch(es).