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You didn't cc the right people at all, which meant I just spent a few hours tracking down and fixing the same bug [0]... PLEASE PLEASE run get_maintainers.pl. For the love of all that's holy. MEMORY MANAGEMENT - THP (TRANSPARENT HUGE PAGE) M: Andrew Morton M: David Hildenbrand M: Lorenzo Stoakes R: Zi Yan R: Baolin Wang R: Liam R. Howlett R: Nico Pache R: Ryan Roberts R: Dev Jain R: Barry Song R: Lance Yang I'm giving review feedback below, so you should respin, but in the next series can you cc everyone above and _please_ make sure the threading works correctly? As I can't even find all the patches in this series properly, it all seems to be broken. On Thu, Feb 26, 2026 at 10:15:31PM +0800, Chris Down wrote: > move_pages_huge_pmd() handles UFFDIO_MOVE for both normal THPs and huge > zero pages. For the huge zero page path, src_folio is explicitly set to > NULL, and is used as a sentinel to skip folio operations like lock and > rmap. > > In the huge zero page branch, src_folio is NULL, so folio_mk_pmd(NULL, > pgprot) passes NULL through folio_pfn() and page_to_pfn(). With > SPARSEMEM_VMEMMAP this silently produces a bogus PFN, installing a PMD > pointing to non-existent physical memory. On other memory models it is a > NULL dereference. > > Use page_folio(src_page) to obtain the valid huge zero folio from the > page, which was obtained from pmd_page() and remains valid throughout. > > Fixes: e3981db444a0 ("mm: add folio_mk_pmd()") > Cc: stable@vger.kernel.org > Signed-off-by: Chris Down > --- > mm/huge_memory.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index 44ff8a648afd..fed57951a7cd 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2794,7 +2794,7 @@ int move_pages_huge_pmd(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, pm > _dst_pmd = pmd_mkwrite(pmd_mkdirty(_dst_pmd), dst_vma); > } else { > src_pmdval = pmdp_huge_clear_flush(src_vma, src_addr, src_pmd); > - _dst_pmd = folio_mk_pmd(src_folio, dst_vma->vm_page_prot); > + _dst_pmd = folio_mk_pmd(page_folio(src_page), dst_vma->vm_page_prot); I prefer my version at [0]. Cleaner to actually pull out the zero_folio into a local variable, and also we should mark it special to be consistent with other codepaths. [0]:https://lore.kernel.org/all/20260302170619.867056-1-lorenzo.stoakes@oracle.com/ > } > set_pmd_at(mm, dst_addr, dst_pmd, _dst_pmd); > > -- > 2.51.2 > > > Thanks, Lorenzo