Re: [PATCH bpf-next v4 2/8] bpf: Associate arena pages with their mapping

["Alexei Starovoitov" <alexei.starovoitov@gmail.com>]

On Wed, Oct 14, 2026 at 11:34 PM Emil Tsalapatis <emil@etsalapatis.com> wrote:
> Associate arena backing pages with the arena's private mapping and set
> their page offsets. This allows the fault handler to delegate user PTE
> installation to generic MM code, which is itself useful for avoiding
> races with kfunc-related arena operations.

arena_vm_fault() returns vmf->page and finish_fault() installs the pte
today. That doesn't need page->mapping. VM_FAULT_LOCKED doesn't either.
tcmu_vma_fault() returns it for alloc_page()-ed pages.
mm folks were removing page->mapping and index from drivers. See
commit 6cdef2ddce2b ("fb_defio: do not use deprecated page->mapping, index fields").

[...]
> +/* Arena pages are not page-cache entries and must not be evicted by MM. */
> +static bool arena_release_folio(struct folio *folio, gfp_t gfp)
> +{
> +	return false;
> +}

The only place that looks at folio->mapping because of VM_FAULT_LOCKED
is PageHWPoison() branch in __do_fault().
If that's the reason for this patch then check PageHWPoison() in
arena_vm_fault() and return VM_FAULT_HWPOISON.
Drop this patch.