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Wed, 10 Sep 2025 19:15:58 -0700 (PDT) Received: from localhost.localdomain ([82.213.227.153]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3e7607cd43csm503301f8f.29.2025.09.10.19.15.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 Sep 2025 19:15:57 -0700 (PDT) From: Andrew Zaborowski X-Google-Original-From: Andrew Zaborowski To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Miaohe Lin Subject: [PATCH] mm: avoid poison consumption when splitting THP Date: Thu, 11 Sep 2025 04:14:01 +0200 Message-ID: <20250911021401.734817-1-balrogg+code@gmail.com> X-Mailer: git-send-email 2.45.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: i1z8o7aahob4qji34izf773mtbr7165u X-Rspamd-Queue-Id: 46860180008 X-Rspam-User: X-Rspamd-Server: rspam03 X-HE-Tag: 1757556960-733707 X-HE-Meta: U2FsdGVkX19NgBONmjaaw7xUC9pbN6HFHHu4/xsLpFr49HZTEbFlVrEpQDeAiqfXfoffQ1/PGiJlUHCvvuEPVvCReEiJhKRTEdCJFxLOOnM6o4kErA1E5Vh63gSkizPAq+RkViETPxm0g1slmf7O4TswmmqB+ZUW15tdNJKimyFucS4tL3OTCZDGiIKnh6yJFuuLu77FGLDP9rBSs7iq1Cby6aPZWoRGGzFocuvCcx5XdjXjH3EvWZCdscxrSG89e86FebtwZbiTMOougRuZw68X7QDTvXJ5+C7RyG0C3OKiTEr3YpPNd8SR6slgzeVKY4VqvIBWf6MC6V+i29go5tDqhDEllo42+PEyQoFmeJQvOYc2zlbhD22kd/N4B78aQogb5q1gT8HXDJlB9Ms5e2abVfxI9UrdRCeO+rRy9+FAekg5Re2/TUo5aZfCi7Ao+6Tbovr4s8Tx1p8WtCKjflMQjvRRpwg+BTqBOcCxMp5zkmriWgTlZkT/HLMGKcV/6P7M4arzW5JEs3+9PBNWOoCsTqdM8Wh4Mzwjkng08xiY40IpWcR5b7R7yh/IDO/YWuK0kol5Bgkq7wtfYBa2i1dog+kRZcgnSl5mpSNVQRZJzHTrtbW1xgBcqjnh8xQb7gAnJZ4JMKIK+Bt4bJtN49/rOjRvYEv76TO1Q0KhWKTgahLzgaFUSFGa/THZnoBiYYN+Gps0z/cSXDrbHH1kW01dqtcF7BmH3PgxYFSlJTLedI/9VvvkGNAVvP1ttQElVrJjCx/AKARe5n/W8Ygk1iUufO96UbiSBZDIzL7fSwawE5L4aSwe4KwCmw2cZXkIf7EFpnDfyGvemZR2/LqqLt3QsA70ICbouxCYhsdjAq3shTwEpzHtmUfIeF9Eq+hmFFH+PUaU1idExJz9fHy6VfT+i5A1N9GDc6ZJ4LS6js5VmpDydvaXOtTouj+Rs4Np08MwmD5GqHhOQT7dxNA XTOYXr6k MbwAfAZs1oVszNMGfij26gHj/W7/EzfJ+sMw9n7L+BFJfViG3AuUW8EI4sfEnmbm8qeIUs7ZdomrgIroCCM5IqNLjs8w2U/0rJEMcEsxVx4LJHWzpbmzswmn9QDuldzqShWeAflManUiCMsUDPKaMGq/SsbCT4/20g40475b+y+dUD1ICiBRynfCyRzk8XxAtfCjzOEIntkr7vC4E07A7l1tLElgmwIma8Ul7e7XHEBcVPAEy9F7l2A/n/JaFqOy3eHZNVhqWpduodz/6tk3VF9r8db0lrWpkbhqlOQWUmtj2mGIPi1FT47av44Yc7vFInt8fkTcve567cXRKUyxD9yRV2n1k8QjzfPkgFdPbxB7A5L5FUrwMgpQRjbGNAQ4I2phyqmx8juQvKCtSbmWVJL6RGjYLJsMp4twK X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Handling a memory failure pointing inside a huge page requires splitting the page. The splitting logic uses a mechanism, implemented in migrate.c:try_to_map_unused_to_zeropage(), that inspects contents of individual pages to find zero-filled pages. The read access to the contents may cause a new, synchronous exception like an x86 Machine Check, delivered before the initial memory_failure() finishes, ending in a crash. Luckily memory_failure() already sets the has_hwpoisoned flag on the folio right before try_to_split_thp_page(). Don't enable the shared zeropage mechanism (RMP_USE_SHARED_ZEROPAGE flag) down in __split_unmapped_folio() when the original folio has has_hwpoisoned. Note: we're disabling a potentially useful feature, some of the individual pages that aren't poisoned might be zero-filled. One argument for not trying to add a mechanism to maybe re-scan them later, apart from code cost, is that the owning process is likely being killed and the memory released. Signed-off-by: Andrew Zaborowski --- mm/huge_memory.c | 3 ++- mm/memory-failure.c | 6 ++++-- 2 files changed, 6 insertions(+), 3 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 9c38a95e9f0..1568f0308b9 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -3588,6 +3588,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order, struct list_head *list, bool uniform_split) { struct deferred_split *ds_queue = get_deferred_split_queue(folio); + bool has_hwpoisoned = folio_test_has_hwpoisoned(folio); XA_STATE(xas, &folio->mapping->i_pages, folio->index); struct folio *end_folio = folio_next(folio); bool is_anon = folio_test_anon(folio); @@ -3858,7 +3859,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order, if (nr_shmem_dropped) shmem_uncharge(mapping->host, nr_shmem_dropped); - if (!ret && is_anon) + if (!ret && is_anon && !has_hwpoisoned) remap_flags = RMP_USE_SHARED_ZEROPAGE; remap_page(folio, 1 << order, remap_flags); diff --git a/mm/memory-failure.c b/mm/memory-failure.c index fc30ca4804b..2d755493de9 100644 --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -2352,8 +2352,10 @@ int memory_failure(unsigned long pfn, int flags) * otherwise it may race with THP split. * And the flag can't be set in get_hwpoison_page() since * it is called by soft offline too and it is just called - * for !MF_COUNT_INCREASED. So here seems to be the best - * place. + * for !MF_COUNT_INCREASED. + * It also tells __split_unmapped_folio() to not bother + * using the shared zeropage -- the all-zeros check would + * consume the poison. So here seems to be the best place. * * Don't need care about the above error handling paths for * get_hwpoison_page() since they handle either free page -- 2.45.2