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mm/huge_memory: set the mmu_gather page size in zap_huge_pud()

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Unmapping a device-dax mapping with 1G alignment on powerpc radix kernel
built with CONFIG_DEBUG_VM triggers this warning on every munmap:

    WARNING: mm/mmu_gather.c:176 at __tlb_remove_folio_pages_size+0x38/0x230
    NIP [c00000000063d508] __tlb_remove_folio_pages_size+0x38/0x230
    LR [c0000000006fb688] zap_huge_pud+0x1b8/0x2d0
    Call Trace:
     zap_huge_pud+0x170/0x2d0 (unreliable)
     __zap_vma_range+0x1604/0x1e20
     unmap_vmas+0xa0/0x1f0
     unmap_region+0xb0/0x130
     vms_complete_munmap_vmas+0x120/0x310
     do_vmi_align_munmap+0x1ec/0x240
     __vm_munmap+0x148/0x220
     sys_munmap+0x28/0x40

To trigger this - it is enough to mmap() /dev/dax0.0, touch the first
byte so that the whole 1G is mapped by a single PUD and then munmap()
it.

PowerPC needs MMU_GATHER_PAGE_SIZE in which mmu_gather needs to record
the page size for which tlb flush is needed. zap_huge_pmd(),
zap_pte_range(), change_huge_pud() etc all do this already. However,
since commit:
  dbe5415329 ("mm/huge_memory: add vmf_insert_folio_pud()")

a device-dax PUD maps a real folio and zap_huge_pud() now hands it to
tlb_remove_page_size(tlb, page, HPAGE_PUD_SIZE). At that point
tlb->page_size is still whatever the previous user left behind, which is
0 for the fresh gather set up by munmap() and so the check fires.

Fix this in the same way like how other similar paths do.

Fixes: dbe5415329 ("mm/huge_memory: add vmf_insert_folio_pud()")
Cc: stable@vger.kernel.org
Reported-by: Pavithra <pavrampu@linux.ibm.com>
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Acked-by: Zi Yan <ziy@nvidia.com>
Acked-by: Muchun Song <muchun.song@linux.dev>
Tested-by: Pavithra Prakash <pavrampu@linux.ibm.com>
Link: https://patch.msgid.link/8b853e5f9f16145859407b28af654b0f79e12642.1793318297.git.ritesh.list@gmail.com
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
This commit is contained in:
Ritesh Harjani (IBM) 2026-10-30 05:37:36 +05:30 committed by David Hildenbrand (Arm)
parent 500624f28e
commit 466d6844c8
1 changed files with 2 additions and 0 deletions
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2
mm/huge_memory.c
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@ -3049,6 +3049,8 @@ int zap_huge_pud(struct mmu_gather *tlb, struct vm_area_struct *vma,
spinlock_t *ptl;
pud_t orig_pud;
tlb_change_page_size(tlb, HPAGE_PUD_SIZE);
ptl = __pud_trans_huge_lock(pud, vma);
if (!ptl)
return 0;