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Sat, 13 Dec 2025 00:01:11 -0800 (PST) Received: from localhost.localdomain ([45.142.165.134]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-29f05287fa3sm53149155ad.5.2025.12.13.00.01.00 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Sat, 13 Dec 2025 00:01:10 -0800 (PST) From: Lance Yang To: akpm@linux-foundation.org Cc: will@kernel.org, aneesh.kumar@kernel.org, npiggin@gmail.com, peterz@infradead.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, arnd@arndb.de, david@kernel.org, lorenzo.stoakes@oracle.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, ioworker0@gmail.com, shy828301@gmail.com, riel@surriel.com, jannh@google.com, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Lance Yang Subject: [PATCH RFC 1/3] mm/tlb: allow architectures to skip redundant TLB sync IPIs Date: Sat, 13 Dec 2025 16:00:23 +0800 Message-ID: <20251213080038.10917-2-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20251213080038.10917-1-lance.yang@linux.dev> References: <20251213080038.10917-1-lance.yang@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: 6C84D16000E X-Rspamd-Server: rspam10 X-Stat-Signature: 7xyhzckb1porsqhre69nq86i7fcbxzua X-HE-Tag: 1765612872-749830 X-HE-Meta: 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 bUvmT/31 zowzX+3aHq2BbgS4QUcDbUYEP2zNFXGGg9EONRUF8pFd4h8LLaVaDAschoz+jZOgv4loWS2BxDiSkx9wz961777okI4EV/qHchbS5A5GVMT1Ku9u+bG1RbUr08zKM3CueHTvxjArxYCUIQzKtt6zFVp60+N6zJGN+onYyY5xcYNuH+1BlcsJwOdDjqH0ZUD2sVR8duvarYTzJBkFiYrdEYJMKm2zSlZ3ISaKRseCJ2fffZXWpTOQeBL7CfYR5ojJ7D2w8OioW53L17ZdYPpKlJs6IvQqKNrABpTYpsNmLSoXc0bts71CqASuRVWP7PB9etVDAfmX+5BpUrmvRBRGqBc6d1YUjn7NUpPMps4xUB9hkxxo5/16WzLPA57fcpyt5O3G2AFNklh7QCe8vDCjk9I3X1J3pqQKw+FmskXL3kdqJmQGejs9RDIkn0jAUGmvCr7nC3lA6WZq1ezesrZ9MB1peig== 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: From: Lance Yang When unsharing hugetlb PMD page tables, we currently send two IPIs: one for TLB invalidation, and another to synchronize with concurrent GUP-fast walkers. However, if the TLB flush already reaches all CPUs, the second IPI is redundant. GUP-fast runs with IRQs disabled, so when the TLB flush IPI completes, any concurrent GUP-fast must have finished. Add tlb_table_flush_implies_ipi_broadcast() to let architectures indicate their TLB flush provides full synchronization, enabling the redundant IPI to be skipped. The default implementation returns false to maintain current behavior. Suggested-by: David Hildenbrand (Red Hat) Signed-off-by: Lance Yang --- include/asm-generic/tlb.h | 22 +++++++++++++++++++++- 1 file changed, 21 insertions(+), 1 deletion(-) diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h index 324a21f53b64..3f0add95604f 100644 --- a/include/asm-generic/tlb.h +++ b/include/asm-generic/tlb.h @@ -248,6 +248,21 @@ static inline void tlb_remove_table(struct mmu_gather *tlb, void *table) #define tlb_needs_table_invalidate() (true) #endif +/* + * Architectures can override if their TLB flush already broadcasts IPIs to all + * CPUs when freeing or unsharing page tables. + * + * Return true only when the flush guarantees: + * - IPIs reach all CPUs with potentially stale paging-structure cache entries + * - Synchronization with IRQ-disabled code like GUP-fast + */ +#ifndef tlb_table_flush_implies_ipi_broadcast +static inline bool tlb_table_flush_implies_ipi_broadcast(void) +{ + return false; +} +#endif + void tlb_remove_table_sync_one(void); #else @@ -829,12 +844,17 @@ static inline void tlb_flush_unshared_tables(struct mmu_gather *tlb) * We only perform this when we are the last sharer of a page table, * as the IPI will reach all CPUs: any GUP-fast. * + * However, if the TLB flush already synchronized with other CPUs + * (indicated by tlb_table_flush_implies_ipi_broadcast()), we can skip + * the additional IPI. + * * Note that on configs where tlb_remove_table_sync_one() is a NOP, * the expectation is that the tlb_flush_mmu_tlbonly() would have issued * required IPIs already for us. */ if (tlb->fully_unshared_tables) { - tlb_remove_table_sync_one(); + if (!tlb_table_flush_implies_ipi_broadcast()) + tlb_remove_table_sync_one(); tlb->fully_unshared_tables = false; } } -- 2.49.0