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Peter Anvin" , , William Kucharski , Vishal Moola , "Alex Williamson" , Peter Xu , , , Eliav Farber Subject: [PATCH 1/4] mm: drop the huge PMD assertion from walk_to_pmd() Date: Wed, 11 Nov 2026 14:06:52 +0000 Message-ID: <20261111140655.34281-2-farbere@amazon.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20261111140655.34281-1-farbere@amazon.com> References: <20261111140655.34281-1-farbere@amazon.com> X-Archived-By: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: EX19D031UWA002.ant.amazon.com (10.13.139.96) To EX19D001UWA001.ant.amazon.com (10.13.138.214) X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 228848000C X-Stat-Signature: n1bzncnjgkccywoca9hgx5xp5fzzk77y X-Rspam-User: X-HE-Tag: 1794406032-344794 X-HE-Meta: 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 dWrCtyHl 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 walk_to_pmd() asserts that the PMD it returns is not a huge entry. That held when commit c2febafc6773 ("mm: convert generic code to 5-level paging") added the assertion: nothing installed a huge PMD over the mappings its callers walk. ARCH_SUPPORTS_HUGE_PFNMAP changed that. A VM_PFNMAP mapping whose driver provides both ->fault and ->huge_fault can have a PMD leaf installed by a concurrent huge fault over the same address, so a caller can observe one and BUG on CONFIG_DEBUG_VM=y. The walk does not need the invariant. pmd_alloc() only allocates when the PUD is empty and otherwise returns pmd_offset(), so a leaf is returned rather than overwritten. Every caller already copes with one, because they all reach pte_offset_map_lock(), which refuses to walk a leaf and returns NULL: insert_pages() turns that into -EFAULT, get_locked_pte() passes the NULL to its callers, and insert_pfn() returns a fault code. Fixes: f9e54c3a2f5b ("vfio/pci: implement huge_fault support") Signed-off-by: Eliav Farber --- mm/memory.c | 1 - 1 file changed, 1 deletion(-) diff --git a/mm/memory.c b/mm/memory.c index ec3d9d99ccee..0f54ee0a6d88 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2384,7 +2384,6 @@ static pmd_t *walk_to_pmd(struct mm_struct *mm, unsigned long addr) if (!pmd) return NULL; - VM_BUG_ON(pmd_trans_huge(*pmd)); return pmd; } -- 2.47.3