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Perez de Azpillaga" , , , Eliav Farber Subject: [PATCH v2 1/4] mm: drop the huge PMD assertion from walk_to_pmd() Date: Thu, 12 Nov 2026 05:14:37 +0000 Message-ID: <20261112051440.16140-2-farbere@amazon.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20261112051440.16140-1-farbere@amazon.com> References: <20261112051440.16140-1-farbere@amazon.com> X-Archived-By: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: EX19D031UWC001.ant.amazon.com (10.13.139.241) To EX19D001UWA001.ant.amazon.com (10.13.138.214) X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 38DFA100003 X-Stat-Signature: ph8x568z4tsg6efrxc4apiouyprzegjh X-Rspam-User: 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-HE-Tag: 1794460494-218882 X-HE-Meta: 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 XtuVM8gn 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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 Reviewed-by: Jose A. Perez de Azpillaga --- 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