6.12-stable review patch. If anyone has any objections, please let me know.
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From: Jinjiang Tu tujinjiang@huawei.com
commit 9f1e8cd0b7c4c944e9921b52a6661b5eda2705ab upstream.
In shrink_folio_list(), the hwpoisoned folio may be large folio, which can't be handled by unmap_poisoned_folio(). For THP, try_to_unmap_one() must be passed with TTU_SPLIT_HUGE_PMD to split huge PMD first and then retry. Without TTU_SPLIT_HUGE_PMD, we will trigger null-ptr deref of pvmw.pte. Even we passed TTU_SPLIT_HUGE_PMD, we will trigger a WARN_ON_ONCE due to the page isn't in swapcache.
Since UCE is rare in real world, and race with reclaimation is more rare, just skipping the hwpoisoned large folio is enough. memory_failure() will handle it if the UCE is triggered again.
This happens when memory reclaim for large folio races with memory_failure(), and will lead to kernel panic. The race is as follows:
cpu0 cpu1 shrink_folio_list memory_failure TestSetPageHWPoison unmap_poisoned_folio --> trigger BUG_ON due to unmap_poisoned_folio couldn't handle large folio
[tujinjiang@huawei.com: add comment to unmap_poisoned_folio()] Link: https://lkml.kernel.org/r/69fd4e00-1b13-d5f7-1c82-705c7d977ea4@huawei.com Link: https://lkml.kernel.org/r/20250627125747.3094074-2-tujinjiang@huawei.com Signed-off-by: Jinjiang Tu tujinjiang@huawei.com Fixes: 1b0449544c64 ("mm/vmscan: don't try to reclaim hwpoison folio") Reported-by: syzbot+3b220254df55d8ca8a61@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/68412d57.050a0220.2461cf.000e.GAE@google.com/ Acked-by: David Hildenbrand david@redhat.com Reviewed-by: Miaohe Lin linmiaohe@huawei.com Acked-by: Zi Yan ziy@nvidia.com Reviewed-by: Oscar Salvador osalvador@suse.de Cc: Kefeng Wang wangkefeng.wang@huawei.com Cc: Michal Hocko mhocko@kernel.org Cc: Oscar Salvador osalvador@suse.de Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/memory-failure.c | 4 ++++ mm/vmscan.c | 8 ++++++++ 2 files changed, 12 insertions(+)
--- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -1559,6 +1559,10 @@ static int get_hwpoison_page(struct page return ret; }
+/* + * The caller must guarantee the folio isn't large folio, except hugetlb. + * try_to_unmap() can't handle it. + */ int unmap_poisoned_folio(struct folio *folio, unsigned long pfn, bool must_kill) { enum ttu_flags ttu = TTU_IGNORE_MLOCK | TTU_SYNC | TTU_HWPOISON; --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1080,6 +1080,14 @@ retry: goto keep;
if (folio_contain_hwpoisoned_page(folio)) { + /* + * unmap_poisoned_folio() can't handle large + * folio, just skip it. memory_failure() will + * handle it if the UCE is triggered again. + */ + if (folio_test_large(folio)) + goto keep_locked; + unmap_poisoned_folio(folio, folio_pfn(folio), false); folio_unlock(folio); folio_put(folio);