Re: [PATCH 2/2] x86/virt/tdx: Use PFN directly for unmapping guest private memory

Edgecombe, Rick P
2026-03-19T18:45:03Z

On Thu, 2026-03-19 at 16:56 +0800, Xiaoyao Li wrote:
> > > >     }
> > > > -void tdx_quirk_reset_page(struct page *page)
> > > > +void tdx_quirk_reset_page(kvm_pfn_t pfn)
> > >
> > > So why keep the function tdx_quirk_reset_page() but expect passing in the
> > > kvm_pfn_t? It looks werid that the name indicates to reset a page but what
> > > gets passed in is a pfn.

The kernel has APIs that take non-struct page arg forms and operate on a "page".
For example free_page(), clear_page(), etc. So keeping the "_page" name seems
not too horrible to me.

> > I thought about introducing tdx_quirk_reset_pfn(). But considering
> > tdx_quirk_reset_pfn() has to be an exported API, I'm reluctant to do that.

Yea exporting two functions that do the same thing doesn't seem the right
balance.

> >
> > Given that even with tdx_quirk_reset_pfn(), it still expects TDX convertible
> > RAM, I think having tdx_quirk_reset_page() to take pfn is still acceptable.
> >
> > We just don't want KVM to do pfn --> struct page --> pfn conversions.

We can assume struct pages have pfn's pretty safely. So pfn->page, and
especially allocated from far away code, is the cleanup target here.

>
> Only tdx_sept_remove_private_spte() is doing such conversions. While
> tdx_reclaim_page() and tdx_reclaim_td_control_pages() already have the
> struct page natively.
>
> So why not considering option 2?
>
>    2. keep tdx_quirk_reset_page() as-is for the cases of
>       tdx_reclaim_page() and tdx_reclaim_td_control_pages() that have the
>       struct page. But only change tdx_sept_remove_private_spte() to use
>       tdx_quirk_reset_paddr() directly.
>
> It will need export tdx_quirk_reset_paddr() for KVM. I think it will be OK?

Exporting tdx_quirk_reset_paddr() seems reasonable, except then we have pfn, PA
and struct page across the API. It increases the asymmetry.

We did discuss converting the whole API over to PFN for symmetry. It could
eliminate the control page and guest memory differences.

But this way seems like a more manageable step that addresses the biggest issue.
If we don't want to do a massive cleanup, there will be some stuff left for the
future.