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d4ec557282
Simplify try_to_unmap_one() by separating the hugetlb parts into try_to_unmap_poisoned_hugetlb_one(). To understand the correctness of the refactoring, the following points are noted: 1. try_to_unmap() is called for hugetlb folios only when they are hwpoisoned. 2. A hugetlb VMA cannot be mlocked. 3. page_vma_mapped_walk() returns at most one hugetlb mapping in a VMA, and that mapping points at the head PFN. 4. We won't ever process a softleaf entry that encodes a hugetlb folio; hugetlb folios are never swapped out, migration entries will be skipped (PVMW_MIGRATION not passed), and device-exclusive does not work for hugetlb. 5. The hwpoison entry is constructed from the poisoned folio, just as in the pre-refactor code. Any previous uffd-wp state is deliberately not preserved for the hwpoison entry. 6. TTU_HWPOISON is always present; for it to not be present, either the folio has to be in swapcache, or mapping_can_writeback() is true (see unmap_poisoned_folio), none of which is true for hugetlb folios. 7. Hugetlb uses separate counters from normal rss counters, therefore update_highwater_rss() need not be called. While at it: - Change VM_BUG_* to VM_WARN_*. - Do not declare variables which are only used once. - Constify some variables. - Add some more VM_WARN_* to assert some invariants. Except the above 4 points, no functional change intended. Link: https://lore.kernel.org/20260730094559.418003-3-dev.jain@arm.com Signed-off-by: Dev Jain <dev.jain@arm.com> Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org> Suggested-by: David Hildenbrand (Arm) <david@kernel.org> Acked-by: David Hildenbrand (Arm) <david@kernel.org> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: Harry Yoo <harry@kernel.org> Cc: Jann Horn <jannh@google.com> Cc: Lance Yang <lance.yang@linux.dev> Cc: Liam R. Howlett <liam@infradead.org> Cc: Muchun Song <muchun.song@linux.dev> Cc: Oscar Salvador <osalvador@suse.de> Cc: Rik van Riel <riel@surriel.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Cc: Vlastimil Babka <vbabka@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>