The patch titled Subject: mm/hwpoison: convert TTU_IGNORE_HWPOISON to TTU_HWPOISON has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-hwpoison-convert-ttu_ignore_hwpoison-to-ttu_hwpoison.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

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: Naoya Horiguchi naoya.horiguchi@nec.com Subject: mm/hwpoison: convert TTU_IGNORE_HWPOISON to TTU_HWPOISON Date: Tue, 21 Feb 2023 17:59:05 +0900

After a memory error happens on a clean folio, a process unexpectedly receives SIGBUS when it accesses to the error page. This SIGBUS killing is pointless and simply degrades the level of RAS of the system, because the clean folio can be dropped without any data lost on memory error handling as we do for a clean pagecache.

When memory_failure() is called on a clean folio, try_to_unmap() is called twice (one from split_huge_page() and one from hwpoison_user_mappings()). The root cause of the issue is that pte conversion to hwpoisoned entry is now done in the first call of try_to_unmap() because PageHWPoison is already set at this point, while it's actually expected to be done in the second call. This behavior disturbs the error handling operation like removing pagecache, which results in the malfunction described above.

So convert TTU_IGNORE_HWPOISON into TTU_HWPOISON and set TTU_HWPOISON only when we really intend to convert pte to hwpoison entry. This can prevent other callers of try_to_unmap() from accidentally converting to hwpoison entries.

Link: https://lkml.kernel.org/r/20230221085905.1465385-1-naoya.horiguchi@linux.dev Fixes: ??? Signed-off-by: Naoya Horiguchi naoya.horiguchi@nec.com Cc: David Hildenbrand david@redhat.com Cc: Hugh Dickins hughd@google.com Cc: Matthew Wilcox willy@infradead.org Cc: Miaohe Lin linmiaohe@huawei.com Cc: Minchan Kim minchan@kernel.org Cc: Vlastimil Babka vbabka@suse.cz Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

include/linux/rmap.h | 2 +- mm/memory-failure.c | 8 ++++---- mm/rmap.c | 2 +- 3 files changed, 6 insertions(+), 6 deletions(-)

--- a/include/linux/rmap.h~mm-hwpoison-convert-ttu_ignore_hwpoison-to-ttu_hwpoison +++ a/include/linux/rmap.h @@ -94,7 +94,7 @@ enum ttu_flags { TTU_SPLIT_HUGE_PMD = 0x4, /* split huge PMD if any */ TTU_IGNORE_MLOCK = 0x8, /* ignore mlock */ TTU_SYNC = 0x10, /* avoid racy checks with PVMW_SYNC */ - TTU_IGNORE_HWPOISON = 0x20, /* corrupted page is recoverable */ + TTU_HWPOISON = 0x20, /* do convert pte to hwpoison entry */ TTU_BATCH_FLUSH = 0x40, /* Batch TLB flushes where possible * and caller guarantees they will * do a final flush if necessary */ --- a/mm/memory-failure.c~mm-hwpoison-convert-ttu_ignore_hwpoison-to-ttu_hwpoison +++ a/mm/memory-failure.c @@ -1034,7 +1034,7 @@ static int me_pagecache_dirty(struct pag * cache and swap cache(ie. page is freshly swapped in). So it could be * referenced concurrently by 2 types of PTEs: * normal PTEs and swap PTEs. We try to handle them consistently by calling - * try_to_unmap(TTU_IGNORE_HWPOISON) to convert the normal PTEs to swap PTEs, + * try_to_unmap(!TTU_HWPOISON) to convert the normal PTEs to swap PTEs, * and then * - clear dirty bit to prevent IO * - remove from LRU @@ -1415,7 +1415,7 @@ static bool hwpoison_user_mappings(struc int flags, struct page *hpage) { struct folio *folio = page_folio(hpage); - enum ttu_flags ttu = TTU_IGNORE_MLOCK | TTU_SYNC; + enum ttu_flags ttu = TTU_IGNORE_MLOCK | TTU_SYNC | TTU_HWPOISON; struct address_space *mapping; LIST_HEAD(tokill); bool unmap_success; @@ -1445,7 +1445,7 @@ static bool hwpoison_user_mappings(struc

if (PageSwapCache(p)) { pr_err("%#lx: keeping poisoned page in swap cache\n", pfn); - ttu |= TTU_IGNORE_HWPOISON; + ttu &= ~TTU_HWPOISON; }

/* @@ -1460,7 +1460,7 @@ static bool hwpoison_user_mappings(struc if (page_mkclean(hpage)) { SetPageDirty(hpage); } else { - ttu |= TTU_IGNORE_HWPOISON; + ttu &= ~TTU_HWPOISON; pr_info("%#lx: corrupted page was clean: dropped without side effects\n", pfn); } --- a/mm/rmap.c~mm-hwpoison-convert-ttu_ignore_hwpoison-to-ttu_hwpoison +++ a/mm/rmap.c @@ -1615,7 +1615,7 @@ static bool try_to_unmap_one(struct foli /* Update high watermark before we lower rss */ update_hiwater_rss(mm);

- if (PageHWPoison(subpage) && !(flags & TTU_IGNORE_HWPOISON)) { + if (PageHWPoison(subpage) && (flags & TTU_HWPOISON)) { pteval = swp_entry_to_pte(make_hwpoison_entry(subpage)); if (folio_test_hugetlb(folio)) { hugetlb_count_sub(folio_nr_pages(folio), mm); _

Patches currently in -mm which might be from naoya.horiguchi@nec.com are

mm-hwpoison-convert-ttu_ignore_hwpoison-to-ttu_hwpoison.patch