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Wed, 04 Nov 2026 03:13:07 -0800 (PST) Received: from fedora ([187.120.134.44]) by smtp.gmail.com with ESMTPSA id 71dfb90a1353d-5eca89b6568sm1403664e0c.1.2026.11.04.03.13.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 04 Nov 2026 03:13:06 -0800 (PST) From: Guilherme Giacomo Simoes To: david@kernel.org Cc: akpm@linux-foundation.org, liam@infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ljs@kernel.org, mhocko@suse.com, rppt@kernel.org, surenb@google.com, trintaeoitogc@gmail.com, vbabka@kernel.org Subject: Re: [PATCH] mm: clear pmd in pmdp_invalidate() Date: Wed, 4 Nov 2026 08:12:54 -0300 Message-ID: <20261104111254.320059-1-trintaeoitogc@gmail.com> X-Mailer: git-send-email 2.52.0 In-Reply-To: References: X-Archived-By: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 704D04000A X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=no autolearn_force=no version=4.0.1 X-Stat-Signature: eh7thh4ry5pu7etgejfqknchukogrp16 X-HE-Tag: 1793790788-863815 X-HE-Meta: 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 KCnYAHQt Zi0tia3duuZRrby825exrkR2mf1YqUAf/5oOyRemaIYqqX1g8cnffsQLyAxCwfMn4S5gSZaA1Gr/XfP6Z4wPGTkw6SZmlLnTmwiLGCj2PqOg48eZcMA05+gnvL4l2WaGbVo4MbQJEmBC5FurZreju/BG5KAuJSphsKeJyJO4y3SLsQWCUjxxchEw3RRXz0RBedY+pZwhm4+wP/TQ7u7VdUf9MiyO4cybxlpc3McUw1nw5ojblKlEHqhdG9gouSbt0hUnh8bWMMGKvTig3X/rgvVR9T38PLGhZcZeYmkeE7t0cUJgcai3P/RQDPeuk3g1UcN3VQhQybL03qctzdNmqiuYXPLp+JtxK7fDbTLK4myHDH9Cb5kXP+UXF/C5tVwLEuzq2hD6Wxme/1xq7GJzhqcp8kJMmFM1lwYFcBxt1DRWs0SXRBPRLkTz9ENcsVuq0jnIjLdYI8k2BzLci3agfGX3oSoilDT4HOdFVhvPM45cl8NI= 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 David, I haved immersed inside this problem on last days, and how sashiko-bot very well apointed, I'm haved doing a wrong duplicated clear on pmd's. I not notice that the pmd_establish() already called the page_table_check_pmd_set() wich in turn call __page_table_check_pmd_clear(), my bad. At first time, I thinked the problem is a duplicated page_table_check_pmd_set(), but with a LLM helpful I ruled out this hypothesis, because I not found any obvious call to page_table_check_pmd_set() before remove_migration_pte(). At second time, I suspicious that maybe we are haved a race condition, that make no sense... After a lot of debug and tests, I found a thing.. And I attempt to test this. If you see inside arch/riscv/include/asm/pgtable.h, the pmd_mkinvalid() do: ``` static inline pmd_t pmd_mkinvalid(pmd_t pmd) { return __pmd(pmd_val(pmd) & ~(_PAGE_PRESENT|_PAGE_PROT_NONE)); } ``` but , the pmd_user_accessible_page() check `pmd_leaf(pmd) && pmd_user(pmd);` and pmd_leaf(): ``` static inline bool pmd_leaf(pmd_t pmd) { return pmd_present(pmd) && (pmd_val(pmd) & _PAGE_LEAF); } ``` and the pmd_present(): ``` #ifdef CONFIG_TRANSPARENT_HUGEPAGE static inline int pmd_present(pmd_t pmd) { /* * Checking for _PAGE_LEAF is needed too because: * When splitting a THP, split_huge_page() will temporarily clear * the present bit, in this situation, pmd_present() and * pmd_trans_huge() still needs to return true. */ return (pmd_val(pmd) & (_PAGE_PRESENT | _PAGE_PROT_NONE | _PAGE_LEAF)); } #else static inline int pmd_present(pmd_t pmd) { return (pmd_val(pmd) & (_PAGE_PRESENT | _PAGE_PROT_NONE)); } #endif ``` And the TRANSPARENT HUGE PAGE , is exactly a page that I was allocated with mmap() (see my previous emails with my repro.c). So, I change the pmd_mkinvalid() adding PAGE_LEAF flag: ``` static inline pmd_t pmd_mkinvalid(pmd_t pmd) { return __pmd(pmd_val(pmd) & ~(_PAGE_PRESENT|_PAGE_PROT_NONE|_PAGE_LEAF)); } ``` And this work for my repro.c. The problem here is what the documentation of pmd_present() say: ``` /* * Checking for _PAGE_LEAF is needed too because: * When splitting a THP, split_huge_page() will temporarily clear * the present bit, in this situation, pmd_present() and * pmd_trans_huge() still needs to return true. */ ``` So the documentation say that if a THP is splitting, this should return true event though PAGE_PRESENT and PAGE_PROT_NONE is cleared. If you think about this, maybe make sense. And after some searchs I saw that was already fixed by Yunhui Cui https://lore.kernel.org/all/20260523042052.35476-1-cuiyunhui@bytedance.com/ Thanks, Guilherme