[PATCH v1 04/13] kho: Verify deserialization status and fix FDT alignment access

[Mike Rapoport]

On Tue, Nov 18, 2025 at 06:11:24PM +0100, Pratyush Yadav wrote:
> On Tue, Nov 18 2025, Pasha Tatashin wrote:
> 
> >> > This page is never freed, so adding it to zone managed pages or keeping it
> >> > reserved does not change anything.
> >>
> >> In practice, sure. I still don't see a good reason to _not_ initialize
> >> the page properly. It's not like it costs us much in terms of
> >> performance or code complexity.
> >>
> >> Since kho_restore_folio() makes sure the folio was _actually_ preserved
> >> from KHO, you have a safety check against previous kernel having a bug
> >> and not preserving the FDT properly. And I get that the FDT has already
> >> been used by this point, but at least you would have some known point to
> >> catch this.
> >
> > The kho_alloc_preserve() API is different from kho_preserve_folio().
> > With kho_preserve_folio(), memory is allocated and some time later is
> > preserved, so there is a possibility for that memory to exist and be
> > used where it is not preserved, therefore it is a crucial step for
> > such memory to also do kho_restore_folio() before used. With
> > kho_alloc_preserve(), when the memory exists it is always preserved;
> > it is gurantee of this API. There is no reason to do
> > kho_restore_folio() on such memory at all. It can be released back to
> > the system via kho_free_restore()/kho_free_unpreserve().
> 
> Even for those I think there should be a kho_restore_mem() or something
> similar (naming things is hard :/), so they go through the restore,
> their struct page is properly initialized and accounted for, and
> make sure the pages were actually preserved.
> 
> Using the memory without restoring it first should be the exception IMO.
 
Base KHO and LUO FTDs are such exceptions for sure :)
We have to use them way before we can even think about restoring.

> -- 
> Regards,
> Pratyush Yadav

-- 
Sincerely yours,
Mike.