+ mm-huge_memory-set-the-mmu_gather-page-size-in-zap_huge_pud.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/huge_memory: set the mmu_gather page size in zap_huge_pud()
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-huge_memory-set-the-mmu_gather-page-size-in-zap_huge_pud.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-huge_memory-set-the-mmu_gather-page-size-in-zap_huge_pud.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: "Ritesh Harjani (IBM)" <ritesh.list@gmail.com>
Subject: mm/huge_memory: set the mmu_gather page size in zap_huge_pud()
Date: Fri, 30 Oct 2026 05:37:36 +0530

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:
  dbe54153296d ("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.

Link: https://lore.kernel.org/8b853e5f9f16145859407b28af654b0f79e12642.1793318297.git.ritesh.list@gmail.com
Fixes: dbe54153296d ("mm/huge_memory: add vmf_insert_folio_pud()")
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reported-by: Pavithra <pavrampu@linux.ibm.com>
Acked-by: Zi Yan <ziy@nvidia.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: <stable@vger.kernel.org>
---

 mm/huge_memory.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/mm/huge_memory.c~mm-huge_memory-set-the-mmu_gather-page-size-in-zap_huge_pud
+++ a/mm/huge_memory.c
@@ -3040,6 +3040,8 @@ int zap_huge_pud(struct mmu_gather *tlb,
 	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;
_

Patches currently in -mm which might be from ritesh.list@gmail.com are

mm-huge_memory-set-the-mmu_gather-page-size-in-zap_huge_pud.patch