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Mon, 26 Oct 2026 15:27:56 +0000 X-Mizu-Trace-ID: b2b5afc969dd0a08 X-Migadu-Flow: FLOW_OUT From: Lance Yang To: alex@ghiti.fr, palmer@dabbelt.com, pjw@kernel.org, aou@eecs.berkeley.edu Cc: akpm@linux-foundation.org, zhangchunyan@iscas.ac.cn, rppt@kernel.org, kas@kernel.org, david@kernel.org, andrew+kernel@donnellan.id.au, rmclure@linux.ibm.com, debug@rivosinc.com, baolin.wang@linux.alibaba.com, usama.arif@linux.dev, wangruikang@iscas.ac.cn, namcao@linutronix.de, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, alexghiti@rivosinc.com, viro@zeniv.linux.org.uk, ajones@ventanamicro.com, arnd@arndb.de, axelrasmussen@google.com, brauner@kernel.org, conor.dooley@microchip.com, conor@kernel.org, jack@suse.cz, liam@infradead.org, ljs@kernel.org, mhocko@suse.com, paul.walmsley@sifive.com, peterx@redhat.com, robh@kernel.org, surenb@google.com, vbabka@kernel.org, yuanchu@google.com, stable@vger.kernel.org, pasha.tatashin@soleen.com, linux-mm@kvack.org, me@ziyao.cc Subject: Re: [PATCH 1/1] riscv/mm: fix soft-dirty migration PMDs being treated as present Date: Mon, 26 Oct 2026 23:27:45 +0800 Message-ID: <20261026152745.11239-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20261004030312.90163-1-lance.yang@linux.dev> References: <20261004030312.90163-1-lance.yang@linux.dev> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 0D2E218000A X-Stat-Signature: zn1kgx4jz9wi8ju7gnakmz1tgf3awmuo X-Rspam-User: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS, SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1793028479-548063 X-HE-Meta: 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 tq8bZKEY sm703qDuaCRi1cTA6XNfWwcbLjvVq9qv4nLxDi09C1eVWxfTC1LdNRmeMCJsmDXQsSQS0uYu5+XOaJw43+2vjl4E6+BGVYfuiquPHpgVGHmt2QaCFwvm5SVmT8Qb+USwUByFLiGuikOR7d0lLy+hehv2At5p6QkGyPz/SVUNe//pjXuIEchHMOFgipAZnpWzSUB+BoVvLBucu8gDAYJQrEzQGLlws2YJgnaKOJecg0vqiN/0PSug/3qadZ2Y9WfnCQcOUmU3rdrhmaQ96S91Yw1ZWVK8MmIXEd2w22L5+uh2AyMb9pfKmIGHay7ha+/GlLc4BolGFC5TOGE5MlXbPsPFbe7tEYG+sPy/ByyeS/0bs4/PBMeLGQGXxvA== 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 Gently ping ... Hi RISC-V folks, any thoughts on the proposed fix? On Sun, Oct 04, 2026 at 11:03:12AM +0800, Lance Yang wrote: >RISC-V uses _PAGE_EXEC for swap soft-dirty tracking when >CONFIG_MEM_SOFT_DIRTY is enabled and Svrsw60t59b is available. That's >a problem for PMD migration entries, since pmd_present() also checks >_PAGE_LEAF (R/W/X) to recognize THPs with _PAGE_PRESENT temporarily >cleared during splitting. > >When a soft-dirty THP is migrated, set_pmd_migration_entry() preserves >soft-dirty with pmd_swp_mksoft_dirty(), setting the X bit in the >migration PMD. Even with _PAGE_PRESENT clear, we end up treating a >migration PMD as a present THP! The fault handler skips >pmd_migration_entry_wait(), and a write fault can end up in >do_huge_pmd_wp_page(), where pmd_page() decodes the migration entry >as a mapped PFN. > >Move the swap soft-dirty bit to bit 12 and start the swap offset at >bit 13 when CONFIG_MEM_SOFT_DIRTY is enabled. This keeps R/W/X clear >in migration PMDs and lets us keep the existing pmd_present() check >for invalidated THPs. Leave the offset at bit 12 when soft-dirty >tracking is disabled. > >Fixes: 2a3ebad4db63 ("riscv: mm: add soft-dirty page tracking support") >Cc: stable@vger.kernel.org >Signed-off-by: Lance Yang >--- >I found this while reviewing Usama's PMD-level swap entries series [1] >and comparing the swap flag bits with the PMD presence checks across >architectures. > >[1] https://lore.kernel.org/all/20261002095503.3585565-1-usama.arif@linux.dev/ > > arch/riscv/include/asm/pgtable-bits.h | 6 +++--- > arch/riscv/include/asm/pgtable.h | 10 ++++++---- > 2 files changed, 9 insertions(+), 7 deletions(-) > >diff --git a/arch/riscv/include/asm/pgtable-bits.h b/arch/riscv/include/asm/pgtable-bits.h >index d5a86b4df3ce6..d84b459e010c1 100644 >--- a/arch/riscv/include/asm/pgtable-bits.h >+++ b/arch/riscv/include/asm/pgtable-bits.h >@@ -27,12 +27,12 @@ > ((riscv_has_extension_unlikely(RISCV_ISA_EXT_SVRSW60T59B)) ? \ > (1UL << 59) : 0) > /* >- * Bit 3 is always zero for swap entry computation, so we >- * can borrow it for swap page soft-dirty tracking. >+ * Bit 12 is reserved for swap soft-dirty tracking. The swap offset >+ * starts at bit 13 when CONFIG_MEM_SOFT_DIRTY is enabled. > */ > #define _PAGE_SWP_SOFT_DIRTY \ > ((riscv_has_extension_unlikely(RISCV_ISA_EXT_SVRSW60T59B)) ? \ >- _PAGE_EXEC : 0) >+ (1UL << 12) : 0) > #else > #define _PAGE_SOFT_DIRTY 0 > #define _PAGE_SWP_SOFT_DIRTY 0 >diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h >index b644db16bda94..acaf6d3b54d04 100644 >--- a/arch/riscv/include/asm/pgtable.h >+++ b/arch/riscv/include/asm/pgtable.h >@@ -1178,18 +1178,20 @@ static inline pud_t pud_modify(pud_t pud, pgprot_t newprot) > * > * Format of swap PTE: > * bit 0: _PAGE_PRESENT (zero) >- * bit 1 to 2: (zero) >- * bit 3: _PAGE_SWP_SOFT_DIRTY >+ * bit 1 to 3: _PAGE_LEAF (zero) > * bit 4: _PAGE_SWP_UFFD > * bit 5: _PAGE_PROT_NONE (zero) > * bit 6: exclusive marker > * bits 7 to 11: swap type >- * bits 12 to XLEN-1: swap offset >+ * bit 12: _PAGE_SWP_SOFT_DIRTY (CONFIG_MEM_SOFT_DIRTY) >+ * bits 12/13 to XLEN-1: swap offset (without/with CONFIG_MEM_SOFT_DIRTY) > */ > #define __SWP_TYPE_SHIFT 7 > #define __SWP_TYPE_BITS 5 > #define __SWP_TYPE_MASK ((1UL << __SWP_TYPE_BITS) - 1) >-#define __SWP_OFFSET_SHIFT (__SWP_TYPE_BITS + __SWP_TYPE_SHIFT) >+#define __SWP_OFFSET_SHIFT \ >+ (__SWP_TYPE_BITS + __SWP_TYPE_SHIFT + \ >+ IS_ENABLED(CONFIG_MEM_SOFT_DIRTY)) > > #define MAX_SWAPFILES_CHECK() \ > BUILD_BUG_ON(MAX_SWAPFILES_SHIFT > __SWP_TYPE_BITS) >-- >2.49.0 > >