Re: [RFC PATCH 4/4] kho: Introduce kho_split_preserved_pages() helper

[Samiullah Khawaja]

On Tue, Jul 07, 2026 at 11:28:28AM +0300, Mike Rapoport wrote:
> > A driver may need to split a high-order allocation that has already
> > been preserved. If the pages are split using split_page() manually,
>
> Why?
> Are there particular examples?
>
> > the refcounts would change but KHO won't record the change in the
> > preserved page-type, resulting in a metadata mismatch during
> > restoration in the new kernel.
> >
> > Introduce kho_split_preserved_pages() to handle splitting of preserved
> > pages. The helper follows an unpreserve -> split -> re-preserve sequence,
> > while ensuring that the KHO radix tree is updated with the correct
> > KHO_PAGE_SPLIT type bits.
> >
> > The helper returns 0 on success, or a negative error code if the
> > re-preservation fails. Callers must ensure the provided order matches
> > the original allocation and that the operation is serialized against
> > other preservation API calls.
>
> Let's put this on hold until there are actual users.

+1

I think we discussed in this in one of the hypervisor liveudpate meeting
sessions and it was concluded that the split of preseved pages is not
needed.
> --
> Sincerely yours,
> Mike.