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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1782923654; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=S8EN7g6oxS7SXD5LHkfE9wVI24o1Ccmyer7oaOUmqbs=; b=iDTr5a4c5GYQEsX7/WoMX8mugZgns0NLjQHuSMmfFNbqMBJ90bt7Imb/Jq2IOUZYVlwefW shL1UB/bB76qXBYtmjfnVFKuf25AHcO7V/mcp3fAWkfsOqbv+UlS8VdUr2ffq/juIgD45a 6Z4SkIcRx2UjYuHcQ0+MYeDPb/uf1Oc= From: Lance Yang To: david@kernel.org, klarasmodin@gmail.com Cc: richard.weiyang@gmail.com, akpm@linux-foundation.org, ljs@kernel.org, riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, balbirs@nvidia.com, sj@kernel.org, ziy@nvidia.com, lance.yang@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [Patch mm-hotfixes v5] mm/page_vma_mapped: fix device-private PMD handling Date: Thu, 2 Jul 2026 00:33:56 +0800 Message-Id: <20260701163356.22936-1-lance.yang@linux.dev> In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Stat-Signature: hy7bqi9pqu673fni7c1bef855zsmgo14 X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 456D81C000B X-HE-Tag: 1782923656-459082 X-HE-Meta: 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PF5hKWCCYGigPr93vNSqMYfYxd6utO5ZO5O6ijEn/HLQlLLAfeqk9CAlM655v8ueeVhgEtmxpHSjmTbeELNVfgUZtvn9qs+Ow1CZeHePvQ3dFxwf9w141PTbdkt/HoalVKbECElE0nSlOzbC+Gmg3kWe1FHJyf2Fp93StaGBXFAw9oIwyBx0yP0h1PDSoDme/izdp8KS1gDBtglGiCbE9/6f9yp38Z3cZfKBU05HDQe4X688Qe5cz10s+6V64oklO4mjK2+/I8XUpqeodYm0TT9FIjTSNsAdgVrVK/LKQ26IgUPJUEowe47GF4pYNoEvB4EVcq/h/8PLFCc4rhP1QJirVOdH2c5KI4tBFuv0NRHEz2r7a4KeckvTXrb69gvUKee5gwKLDLCofN5aW7dUmH49agHEPQ7aFDflzrrdm+P9p69Q= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Jul 01, 2026 at 05:36:33PM +0200, David Hildenbrand (Arm) wrote: >On 7/1/26 16:33, Klara Modin wrote: >> Hi, Hi, [...] >> >> This results in a build bug for my Raspberry Pi 1: Thanks for reporting this! >> In file included from : >> In function ‘check_pmd’, >> inlined from ‘page_vma_mapped_walk’ at /home/klara/git/linux/trees/bisect/mm/page_vma_mapped.c:256:10: >> /home/klara/git/linux/trees/bisect/include/linux/compiler_types.h:702:45: error: call to ‘__compiletime_assert_433’ declared with attribute error: BUILD_BUG failed >> 702 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) >> | ^ >> /home/klara/git/linux/trees/bisect/include/linux/compiler_types.h:683:25: note: in definition of macro ‘__compiletime_assert’ >> 683 | prefix ## suffix(); \ >> | ^~~~~~ >> /home/klara/git/linux/trees/bisect/include/linux/compiler_types.h:702:9: note: in expansion of macro ‘_compiletime_assert’ >> 702 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) >> | ^~~~~~~~~~~~~~~~~~~ >> /home/klara/git/linux/trees/bisect/include/linux/build_bug.h:40:37: note: in expansion of macro ‘compiletime_assert’ >> 40 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg) >> | ^~~~~~~~~~~~~~~~~~ >> /home/klara/git/linux/trees/bisect/include/linux/build_bug.h:60:21: note: in expansion of macro ‘BUILD_BUG_ON_MSG’ >> 60 | #define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed") >> | ^~~~~~~~~~~~~~~~ >> /home/klara/git/linux/trees/bisect/include/linux/huge_mm.h:113:28: note: in expansion of macro ‘BUILD_BUG’ >> 113 | #define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; }) >> | ^~~~~~~~~ >> /home/klara/git/linux/trees/bisect/include/linux/huge_mm.h:117:26: note: in expansion of macro ‘HPAGE_PMD_SHIFT’ >> 117 | #define HPAGE_PMD_ORDER (HPAGE_PMD_SHIFT-PAGE_SHIFT) >> | ^~~~~~~~~~~~~~~ >> /home/klara/git/linux/trees/bisect/include/linux/huge_mm.h:118:26: note: in expansion of macro ‘HPAGE_PMD_ORDER’ >> 118 | #define HPAGE_PMD_NR (1<> | ^~~~~~~~~~~~~~~ >> /home/klara/git/linux/trees/bisect/mm/page_vma_mapped.c:142:20: note: in expansion of macro ‘HPAGE_PMD_NR’ >> 142 | if ((pfn + HPAGE_PMD_NR - 1) < pvmw->pfn) >> | ^~~~~~~~~~~~ >> >> bisect log: >> >> # bad: [be5c93fa674f0fc3c8f359c2143abce6bbb422e6] Add linux-next specific files for 20260630 >> git bisect start 'HEAD' >> # status: waiting for 'good' commit(s), 'bad' commit known >> # good: [dc59e4fea9d83f03bad6bddf3fa2e52491777482] Linux 7.2-rc1 >> git bisect good dc59e4fea9d83f03bad6bddf3fa2e52491777482 >> # bad: [6148219e90732fd06f5d7a498bda974e6a43ab4b] Merge branch 'nand/next' of https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git >> git bisect bad 6148219e90732fd06f5d7a498bda974e6a43ab4b >> # bad: [e0326ebe10191447ab8fa2e904080df7b743765e] Merge branch 'for-next' of https://git.kernel.org/pub/scm/linux/kernel/git/soc/soc.git >> git bisect bad e0326ebe10191447ab8fa2e904080df7b743765e >> # bad: [fbc9c5ac47cef5a2b04aef30c8e990b32dcf2548] Merge branch 'hwmon' of https://git.kernel.org/pub/scm/linux/kernel/git/groeck/linux-staging.git >> git bisect bad fbc9c5ac47cef5a2b04aef30c8e990b32dcf2548 >> # bad: [e488171f6f6df6fc899a355079665fdb3c50b0e3] Merge branch 'for-linus' of https://git.kernel.org/pub/scm/linux/kernel/git/broonie/sound.git >> git bisect bad e488171f6f6df6fc899a355079665fdb3c50b0e3 >> # bad: [60db0fcb8fc9d80ac0b63041c632b41a311a45f1] Merge branch 'fs-current' of linux-next >> git bisect bad 60db0fcb8fc9d80ac0b63041c632b41a311a45f1 >> # good: [51021d260d682aa17b3533848a99160ab83e0c93] Merge branch 'vfs.fixes' of https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git >> git bisect good 51021d260d682aa17b3533848a99160ab83e0c93 >> # good: [ded56474db6552260786a65898322464b72c7540] mm: a second pagecache maintainer >> git bisect good ded56474db6552260786a65898322464b72c7540 >> # good: [6c893b948351d42cfc3761cc746ab5b3d03ee7f3] Merge branch 'misc-7.2' into next-fixes >> git bisect good 6c893b948351d42cfc3761cc746ab5b3d03ee7f3 >> # good: [bfcc55a14179495b0c41408908fd7b9d7785c694] lib: test_hmm: use device devt for coherent device range selection >> git bisect good bfcc55a14179495b0c41408908fd7b9d7785c694 >> # good: [a27318567c92ba5482906d047e71a7aa4fd01889] Merge branch 'fixes' of https://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git >> git bisect good a27318567c92ba5482906d047e71a7aa4fd01889 >> # bad: [6887a39652cdfd4cfd3b0962662c9cbc26ce5252] mm/page_vma_mapped: fix device-private PMD handling >> git bisect bad 6887a39652cdfd4cfd3b0962662c9cbc26ce5252 >> # good: [2cc6bd0efc264b9ac760c2bc74dff4f521a680a1] MAINTAINERS: s/SeongJae/SJ/ >> git bisect good 2cc6bd0efc264b9ac760c2bc74dff4f521a680a1 >> # first 'bad' commit: [6887a39652cdfd4cfd3b0962662c9cbc26ce5252] mm/page_vma_mapped: fix device-private PMD handling >> >>> >>> Fixes: 65edfda6f3f2 ("mm/rmap: extend rmap and migration support device-private entries") >>> Cc: >>> Signed-off-by: Wei Yang >>> Suggested-by: David Hildenbrand >>> Cc: David Hildenbrand >>> Cc: Balbir Singh >>> Cc: SeongJae Park >>> Cc: Zi Yan >>> Cc: Lorenzo Stoakes >>> Cc: Lance Yang >>> >>> --- >>> v5: >>> * put device-private pmd handling along with the other two cases >>> * remove thp_migration_supported() >>> v4: https://lore.kernel.org/all/20260624065353.1622-1-richard.weiyang@gmail.com/T/#u >>> * refine subject and commit log based on Lorenzo's suggestion >>> * put pmd device-private entry handling in its own if branch, >>> suggested by Lorenzo >>> >>> v3: >>> * remove cleanup part, only fix the issue for device-private entry >>> * refine user effect description based on Lorenzo's suggestion >>> >>> v2: https://lore.kernel.org/all/20260616063436.20455-1-richard.weiyang@gmail.com/T/#u >>> * specify the possible error case of current code and user visible effect >>> * besides fix, cleanup the pmd entry handling based on David's suggestion >>> >>> v1: https://lore.kernel.org/linux-mm/20260508013728.21285-1-richard.weiyang@gmail.com/ >>> --- >>> mm/page_vma_mapped.c | 30 ++++++++++++++++-------------- >>> 1 file changed, 16 insertions(+), 14 deletions(-) >>> >>> diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c >>> index 2ccbabfb2cc1..2d6c58488e3a 100644 >>> --- a/mm/page_vma_mapped.c >>> +++ b/mm/page_vma_mapped.c >>> @@ -243,21 +243,30 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) >>> */ >>> pmde = pmdp_get_lockless(pvmw->pmd); >>> >>> - if (pmd_trans_huge(pmde) || pmd_is_migration_entry(pmde)) { >>> + if (pmd_trans_huge(pmde) || pmd_is_migration_entry(pmde) || >>> + pmd_is_device_private_entry(pmde)) { >>> pvmw->ptl = pmd_lock(mm, pvmw->pmd); >>> pmde = *pvmw->pmd; >>> - if (!pmd_present(pmde)) { >>> + if (pmd_is_migration_entry(pmde)) { >>> softleaf_t entry; >>> >>> - if (!thp_migration_supported() || >>> - !(pvmw->flags & PVMW_MIGRATION)) >>> + if (!(pvmw->flags & PVMW_MIGRATION)) >>> return not_found(pvmw); >>> entry = softleaf_from_pmd(pmde); >>> + if (!check_pmd(softleaf_to_pfn(entry), pvmw)) >>> + return not_found(pvmw); >>> + return true; >>> + } else if (pmd_is_device_private_entry(pmde)) { >>> + softleaf_t entry; >>> >> >>> - if (!softleaf_is_migration(entry) || >>> - !check_pmd(softleaf_to_pfn(entry), pvmw)) >> >> My only guess here would be that the compiler evaluates >> !softleaf_is_migration(entry) to always be true and optimises away the >> !check_pmd(softleaf_to_pfn(entry), pvmw) which is why this worked >> before? > >Weird, we enter this path only with > >pmd_trans_huge(pmde) || pmd_is_migration_entry(pmde) || >pmd_is_device_private_entry(pmde) > >If any one of these would compile for !CONFIG_TRANSPARENT_HUGEPAGE that would be >odd. > >pmd_is_device_private_entry() is hard-coded to false unless >CONFIG_ARCH_ENABLE_THP_MIGRATION. Which is only selected with >ARCH_ENABLE_THP_MIGRATION. > >pmd_trans_huge() as well. > >Maybe it's struggling with pmd_is_migration_entry() on some (older) compilers? >(not innlining stuff and not properly optimizing it out). > >The whole conditional must be optimized out. Right. Kinda weird if compiler didn't fold pmd_trans_huge(pmde) || pmd_is_migration_entry(pmde) || pmd_is_device_private_entry(pmde) away here ... >We could check for IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) right at the start >to make it easier for the compiler: +1, explicit THP guard should do the trick :) >if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) && > (pmd_trans_huge(pmde) || pmd_is_migration_entry(pmde) || > pmd_is_device_private_entry(pmde))) { > > Klara, could you try with this change and see if it fixes the build? Thanks, Lance