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

[Samiullah Khawaja <skhawaja@google.com>]

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.
>