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mm/mremap: fix moving PUD leaves

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pud_none_or_clear_bad() only really works on page tables. PUD leaves
confuse the check and make us clear the page table entry and print a
warning.

Since commit aed877c2b4 ("device/dax: properly refcount device dax pages
when mapping"), this also leaks device-DAX folio references, mapcounts
and RSS accounting, resulting in "Bad rss-counter state" warnings on exit.

Allow PUD leaves in get_old_pud(). If a PUD leaf cannot be moved as a
whole or the move fails, split it. This unmaps it with proper accounting
instead of treating the leaf entry as a PMD table.

Keep using pud_trans_huge() for now, in the future this code should be
cleaned up to just check for PUD leaves.

Fix generated by an LLM and sent by Josef Bacik in private.

Fixes: a00cc7d9dd ("mm, x86: add support for PUD-sized transparent hugepages")
Cc: stable@vger.kernel.org
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
[ david: fallthrough after splitting ]
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Tested-by: Muhammad Usama Anjum <usama.anjum@arm.com>
Link: https://patch.msgid.link/20261031-fixes_core-v3-32-d6437171ecc3@kernel.org
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
This commit is contained in:
Josef Bacik 2026-10-31 10:40:01 +01:00 committed by David Hildenbrand (Arm)
parent 402882943d
commit 440c877975
1 changed files with 4 additions and 5 deletions
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9
mm/mremap.c
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@ -87,7 +87,7 @@ static pud_t *get_old_pud(struct mm_struct *mm, unsigned long addr)
return NULL;
pud = pud_offset(p4d, addr);
if (pud_none_or_clear_bad(pud))
if (!pud_trans_huge(*pud) && pud_none_or_clear_bad(pud))
return NULL;
return pud;
@ -847,11 +847,10 @@ unsigned long move_page_tables(struct pagetable_move_control *pmc)
if (!new_pud)
break;
if (pud_trans_huge(*old_pud)) {
if (extent == HPAGE_PUD_SIZE) {
move_pgt_entry(pmc, HPAGE_PUD, old_pud, new_pud);
/* We ignore and continue on error? */
if (extent == HPAGE_PUD_SIZE &&
move_pgt_entry(pmc, HPAGE_PUD, old_pud, new_pud))
continue;
}
split_huge_pud(pmc->old, old_pud, pmc->old_addr);
} else if (IS_ENABLED(CONFIG_HAVE_MOVE_PUD) && extent == PUD_SIZE) {
if (move_pgt_entry(pmc, NORMAL_PUD, old_pud, new_pud))
continue;