From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6899F1DA60D; Thu, 30 Jul 2026 01:03:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785373411; cv=none; b=cgoX1GK2Co7iar5YkVtHzLHvE0mwP93kqyMvfoPSJvyDCA9/M7HievK9mSyKSLpA4zuro431YYc1GmlDM6q3fCx4bpI4bJxpzGAMKYMIgw3RoagwxwwbM0Av/z6kVbbUo4GC7+gv9+WOCzAzP47dN9a3sQpIMQwD5Te5rFvxM28= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785373411; c=relaxed/simple; bh=k453IVbu8RQ1leYA5Ocaovg3D4tIcROHtR6CEKUIGSM=; h=Date:To:From:Subject:Message-Id; b=EM5slRl+mBz1WU8eMowFqDwa4Ay4tTjEIvABwZYo+2iIfeiapUph4O8fB+yxiYBOa4rGIzsbQfz9J+xa/MUlQB3JcLsWbHAEmLQxgWWfOhgzpFRy1aA8gKt51F44VQvogQ6mrXkoqNZeBXbJdYRD91qms9VDSEMy6od9n159QvA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=bqIDVg0Q; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="bqIDVg0Q" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E714A1F000E9; Thu, 30 Jul 2026 01:03:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1785373409; bh=8o8nHY43O/SZeCDhEe5bQPkl5GscGH3HALrQ4n/k3Sg=; h=Date:To:From:Subject; b=bqIDVg0QYNG289Rtubwe3pE8MVr6cdityIHyAWrKOK3ca5yKGhkciuhdS86OMKdQN OtgiL799J+r5hrbrH7ew/pQAgZ3O0nnFHf/i9dbXdZrP+/amzkUk6EOuvc55MnOrJ6 6l7IvpiRh6eL8a85kuePF6/XObO3z7uTQFVtVfuI= Date: Wed, 29 Jul 2026 18:03:28 -0700 To: mm-commits@vger.kernel.org,ziy@nvidia.com,xueyuan.chen@vivo.com,uqbarz@gmail.com,stable@vger.kernel.org,shy828301@gmail.com,ryan.roberts@arm.com,p.raghav@samsung.com,npache@redhat.com,liam@infradead.org,lance.yang@linux.dev,kas@kernel.org,hughd@google.com,hare@suse.de,dev.jain@arm.com,david@kernel.org,baolin.wang@linux.alibaba.com,baohua@kernel.org,ljs@kernel.org,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-huge_memory-separate-out-config_persistent_huge_zero_folio-logic.patch added to mm-new branch Message-Id: <20260730010328.E714A1F000E9@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm/huge_memory: separate out CONFIG_PERSISTENT_HUGE_ZERO_FOLIO logic has been added to the -mm mm-new branch. Its filename is mm-huge_memory-separate-out-config_persistent_huge_zero_folio-logic.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-huge_memory-separate-out-config_persistent_huge_zero_folio-logic.patch This patch will later appear in the mm-new branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Note, mm-new is a provisional staging ground for work-in-progress patches, and acceptance into mm-new is a notification for others take notice and to finish up reviews. Please do not hesitate to respond to review feedback and post updated versions to replace or incrementally fixup patches in mm-new. The mm-new branch of mm.git is not included in linux-next If a few days of testing in mm-new is successful, the patch will me moved into mm.git's mm-unstable branch, which is included in linux-next Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: "Lorenzo Stoakes (ARM)" Subject: mm/huge_memory: separate out CONFIG_PERSISTENT_HUGE_ZERO_FOLIO logic Date: Tue, 28 Jul 2026 13:05:44 +0100 Patch series "mm/huge_memory: fix huge_zero_pfn race". There is a subtle race in the reference-counted huge_zero_folio implementation. The fast path atomic logic fails to account for the fact that the shrinker (which drops the final huge_zero_refcount pin) can overwrite huge_zero_pfn with the ~0UL sentinel value in shrink_huge_zero_folio_scan() after a racing get_huge_zero_folio() installed a valid value there. This results in huge_zero_folio being correctly set but huge_zero_pfn being set incorrectly and thus is_huge_zero_pfn() and consequently is_huge_zero_pmd() will misidentify the huge zero folio as being an ordinary THP folio. This can result in the huge zero folio being split and otherwise treated incorrectly. The solution to this is very subtle as there is an atomic fast path, and thus ordering in weakly ordered architectures has to be treated very carefully. As a result, this series first reworks the CONFIG_PERSISTENT_HUGE_ZERO_FOLIO logic so it is separated from the refcounted code in order to make the subsequent fix reasonably understandable. The second commit fixes the issue by introducing a spinlock around huge_zero_[pfn, folio, refcount] write, with careful consideration paid to load/store ordering in the fast path. This patch (of 2): Rather than mixing the refcounted and non-refcounted CONFIG_PERSISTENT_HUGE_ZERO_FOLIO logic, separate the two out cleanly so it is clear what happens when this configuration option is set and what happens when it is not. Introduce HUGE_ZERO_UNSET_PFN to abstract the ~0UL assignment, only introduce the refcount and shrinker if !CONFIG_PERSISTENT_HUGE_ZERO_FOLIO, abstract initialisation and teardown, abstract the huge zero folio allocation from refcounting. Also change a BUG_ON() to WARN_ON_ONCE() while we're at it. Without this change, the subsequent fix for a subtle race is harder to understand thus this is a dependency of it. Link: https://lore.kernel.org/20260728-fix-refcounted-huge-zero-v1-1-3f261f5447b4@kernel.org Fixes: 3b77e8c8cde5 ("mm/thp: make is_huge_zero_pmd() safe and quicker") Signed-off-by: Lorenzo Stoakes (ARM) Cc: Baolin Wang Cc: Barry Song Cc: David Hildenbrand Cc: Dev Jain Cc: Hannes Reinecke Cc: Hugh Dickins Cc: Kiryl Shutsemau Cc: Lance Yang Cc: Liam R. Howlett Cc: Nico Pache Cc: Pankaj Raghav Cc: Ryan Roberts Cc: Yang Shi Cc: Zi Yan Cc: Hengbin Zhang Cc: Xueyuan Chen Cc: # 6.18.x: dependency of subsequent fix Signed-off-by: Andrew Morton --- mm/huge_memory.c | 159 ++++++++++++++++++++++++++------------------- 1 file changed, 94 insertions(+), 65 deletions(-) --- a/mm/huge_memory.c~mm-huge_memory-separate-out-config_persistent_huge_zero_folio-logic +++ a/mm/huge_memory.c @@ -77,9 +77,14 @@ static unsigned long deferred_split_scan struct shrink_control *sc); static bool split_underused_thp = true; -static atomic_t huge_zero_refcount; +#define HUGE_ZERO_UNSET_PFN (~0UL) struct folio *huge_zero_folio __read_mostly; -unsigned long huge_zero_pfn __read_mostly = ~0UL; +unsigned long huge_zero_pfn __read_mostly = HUGE_ZERO_UNSET_PFN; +#ifndef CONFIG_PERSISTENT_HUGE_ZERO_FOLIO +static atomic_t huge_zero_refcount; +static struct shrinker *huge_zero_folio_shrinker; +#endif + unsigned long huge_anon_orders_always __read_mostly; unsigned long huge_anon_orders_madvise __read_mostly; unsigned long huge_anon_orders_inherit __read_mostly; @@ -221,22 +226,58 @@ unsigned long __thp_vma_allowable_orders return orders; } -static bool get_huge_zero_folio(void) +static struct folio *alloc_huge_zero_folio(void) { struct folio *zero_folio; -retry: - if (likely(atomic_inc_not_zero(&huge_zero_refcount))) - return true; zero_folio = folio_alloc((GFP_TRANSHUGE | __GFP_ZERO | __GFP_ZEROTAGS) & ~__GFP_MOVABLE, HPAGE_PMD_ORDER); if (!zero_folio) { count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED); - return false; + return NULL; + } + folio_clear_large_rmappable(zero_folio); /* Explicitly not rmappable. */ + return zero_folio; +} + +#ifdef CONFIG_PERSISTENT_HUGE_ZERO_FOLIO +static int __init huge_zero_init(void) +{ + huge_zero_folio = alloc_huge_zero_folio(); + if (!huge_zero_folio) { + pr_warn("Allocating persistent huge zero folio failed\n"); + } else { + huge_zero_pfn = folio_pfn(huge_zero_folio); + count_vm_event(THP_ZERO_PAGE_ALLOC); } - /* Ensure zero folio won't have large_rmappable flag set. */ - folio_clear_large_rmappable(zero_folio); + return 0; +} + +static void __init huge_zero_shrinker_exit(void) +{ +} + +struct folio *mm_get_huge_zero_folio(struct mm_struct *mm) +{ + return huge_zero_folio; +} + +void mm_put_huge_zero_folio(struct mm_struct *mm) +{ +} +#else +static bool get_huge_zero_folio(void) +{ + struct folio *zero_folio; +retry: + if (likely(atomic_inc_not_zero(&huge_zero_refcount))) + return true; + + zero_folio = alloc_huge_zero_folio(); + if (unlikely(!zero_folio)) + return false; + preempt_disable(); if (cmpxchg(&huge_zero_folio, NULL, zero_folio)) { preempt_enable(); @@ -258,33 +299,7 @@ static void put_huge_zero_folio(void) * Counter should never go to zero here. Only shrinker can put * last reference. */ - BUG_ON(atomic_dec_and_test(&huge_zero_refcount)); -} - -struct folio *mm_get_huge_zero_folio(struct mm_struct *mm) -{ - if (IS_ENABLED(CONFIG_PERSISTENT_HUGE_ZERO_FOLIO)) - return huge_zero_folio; - - if (mm_flags_test(MMF_HUGE_ZERO_FOLIO, mm)) - return READ_ONCE(huge_zero_folio); - - if (!get_huge_zero_folio()) - return NULL; - - if (mm_flags_test_and_set(MMF_HUGE_ZERO_FOLIO, mm)) - put_huge_zero_folio(); - - return READ_ONCE(huge_zero_folio); -} - -void mm_put_huge_zero_folio(struct mm_struct *mm) -{ - if (IS_ENABLED(CONFIG_PERSISTENT_HUGE_ZERO_FOLIO)) - return; - - if (mm_flags_test(MMF_HUGE_ZERO_FOLIO, mm)) - put_huge_zero_folio(); + WARN_ON_ONCE(atomic_dec_and_test(&huge_zero_refcount)); } static unsigned long shrink_huge_zero_folio_count(struct shrinker *shrink, @@ -300,7 +315,7 @@ static unsigned long shrink_huge_zero_fo if (atomic_cmpxchg(&huge_zero_refcount, 1, 0) == 1) { struct folio *zero_folio = xchg(&huge_zero_folio, NULL); BUG_ON(zero_folio == NULL); - WRITE_ONCE(huge_zero_pfn, ~0UL); + WRITE_ONCE(huge_zero_pfn, HUGE_ZERO_UNSET_PFN); folio_put(zero_folio); return HPAGE_PMD_NR; } @@ -308,7 +323,46 @@ static unsigned long shrink_huge_zero_fo return 0; } -static struct shrinker *huge_zero_folio_shrinker; +static int __init huge_zero_init(void) +{ + huge_zero_folio_shrinker = shrinker_alloc(0, "thp-zero"); + if (!huge_zero_folio_shrinker) { + shrinker_free(deferred_split_shrinker); + list_lru_destroy(&deferred_split_lru); + return -ENOMEM; + } + + huge_zero_folio_shrinker->count_objects = shrink_huge_zero_folio_count; + huge_zero_folio_shrinker->scan_objects = shrink_huge_zero_folio_scan; + shrinker_register(huge_zero_folio_shrinker); + return 0; +} + +static void __init huge_zero_shrinker_exit(void) +{ + shrinker_free(huge_zero_folio_shrinker); +} + +struct folio *mm_get_huge_zero_folio(struct mm_struct *mm) +{ + if (mm_flags_test(MMF_HUGE_ZERO_FOLIO, mm)) + return READ_ONCE(huge_zero_folio); + + if (!get_huge_zero_folio()) + return NULL; + + if (mm_flags_test_and_set(MMF_HUGE_ZERO_FOLIO, mm)) + put_huge_zero_folio(); + + return READ_ONCE(huge_zero_folio); +} + +void mm_put_huge_zero_folio(struct mm_struct *mm) +{ + if (mm_flags_test(MMF_HUGE_ZERO_FOLIO, mm)) + put_huge_zero_folio(); +} +#endif /* CONFIG_PERSISTENT_HUGE_ZERO_FOLIO */ #ifdef CONFIG_SYSFS static ssize_t enabled_show(struct kobject *kobj, @@ -970,39 +1024,14 @@ static int __init thp_shrinker_init(void deferred_split_shrinker->scan_objects = deferred_split_scan; shrinker_register(deferred_split_shrinker); - if (IS_ENABLED(CONFIG_PERSISTENT_HUGE_ZERO_FOLIO)) { - /* - * Bump the reference of the huge_zero_folio and do not - * initialize the shrinker. - * - * huge_zero_folio will always be NULL on failure. We assume - * that get_huge_zero_folio() will most likely not fail as - * thp_shrinker_init() is invoked early on during boot. - */ - if (!get_huge_zero_folio()) - pr_warn("Allocating persistent huge zero folio failed\n"); - return 0; - } - - huge_zero_folio_shrinker = shrinker_alloc(0, "thp-zero"); - if (!huge_zero_folio_shrinker) { - shrinker_free(deferred_split_shrinker); - list_lru_destroy(&deferred_split_lru); - return -ENOMEM; - } - - huge_zero_folio_shrinker->count_objects = shrink_huge_zero_folio_count; - huge_zero_folio_shrinker->scan_objects = shrink_huge_zero_folio_scan; - shrinker_register(huge_zero_folio_shrinker); - - return 0; + return huge_zero_init(); } static void __init thp_shrinker_exit(void) { - shrinker_free(huge_zero_folio_shrinker); shrinker_free(deferred_split_shrinker); list_lru_destroy(&deferred_split_lru); + huge_zero_shrinker_exit(); } static int __init hugepage_init(void) _ Patches currently in -mm which might be from ljs@kernel.org are mm-vmalloc-acquire-init_mm-lock-on-huge-vmap-to-avoid-ptdump-uaf.patch mm-ptdump-always-stabilise-against-page-table-freeing-using-init_mm.patch arm64-remove-redundant-concurrent-ptdump-uaf-mitigation.patch x86-mm-pat-acquire-init_mm-write-lock-on-collapse-to-avoid-uaf.patch x86-mm-pat-acquire-init_mm-read-lock-on-attribute-change-to-avoid-uaf.patch x86-mm-pat-allocate-split-page-tables-as-kernel-page-tables.patch mm-move-vma_start_pgoff-into-mmh-and-clean-up.patch mm-add-kdoc-comments-for-vma_start-last_pgoff.patch tools-testing-vma-use-vma_start_pgoff-in-merge-tests.patch mm-introduce-and-use-vma_end_pgoff.patch mm-rmap-update-mm-interval_treec-comments.patch mm-rmap-parameterise-vma_interval_tree_-by-address_space.patch mm-rmap-elide-unnecessary-static-inlines-in-interval_treec.patch mm-rmap-rename-vma_interval_tree_-to-mapping_rmap_tree_.patch mm-rmap-parameterise-anon_vma_interval_tree_-by-anon_vma.patch mm-rmap-rename-anon_vma_interval_tree_-params-and-use-pgoff_t.patch mm-rmap-rename-anon_vma_interval_tree_-to-anon_rmap_tree_.patch maintainers-move-mm-interval_treec-to-rmap-section.patch mm-vma-introduce-and-use-vmg_pages-vmg__pgoff.patch mm-vma-clean-up-anon_vma_compatible.patch mm-vma-refactor-vmg_adjust_set_range-for-clarity.patch mm-vma-minor-cleanup-of-expand_.patch mm-introduce-and-use-linear_page_delta.patch mm-vma-use-vma_start_pgoff-linear_page_index-in-mm-code.patch mm-prefer-vma__pgoff-to-vma-vm_pgoff-in-kernel.patch mm-vma-remove-duplicative-vma_pgoff_offset-helper.patch mm-use-linear_page_-consistently.patch mm-vma-introduce-vma_assert_can_modify.patch mm-vma-add-and-use-vma__pgoff.patch mm-vma-move-__install_special_mapping-to-vmac.patch mm-vma-make-vma_set_range-static-drop-insert_vm_struct-decl.patch mm-vma-update-vma_shrink-to-not-pass-start-pgoff-parameters.patch mm-vma-update-vmg_adjust_set_range-to-offset-pgoff-instead.patch mm-vma-slightly-rework-the-anonymous-check-in-__mmap_new_vma.patch mm-vma-introduce-and-use-vma_set_pgoff.patch mm-vma-correct-incorrect-vmah-inclusion.patch mm-vma-use-guard-clauses-in-can_vma_merge_.patch tools-testing-vma-default-vma-mm-flag-bits-to-64-bit.patch tools-testing-vma-output-compared-expression-on-assert_.patch mm-introduce-vma_flags_can_grow-and-vma_can_grow.patch mm-vma-update-do_mmap-to-use-vma_flags_t.patch mm-convert-__get_unmapped_area-to-use-vma_flags_t.patch mm-update-generic_get_unmapped_area-to-use-vma_flags_t.patch mm-prefer-mm-def_vma_flags-in-mm-logic.patch mm-vma-convert-vm_pgprot_modify-to-use-vma_flags_t-and-rename.patch mm-vma-rename-vma_get_page_prot-to-vma_flags_to_page_prot.patch mm-introduce-vma_get_page_prot-and-use-it.patch mm-vma-update-create_init_stack_vma-to-use-vma_flags_t.patch mm-vma-convert-miscellaneous-uses-of-vma-flags-in-core-mm.patch mm-mlock-convert-mlock-code-to-use-vma_flags_t.patch mm-mprotect-convert-mprotect-code-to-use-vma_flags_t.patch mm-mremap-convert-mremap-code-to-use-vma_flags_t.patch mm-mseal-remove-superfluous-comments-fix-confusion-around-mm.patch mm-mseal-limit-scope-of-mseal-address-zero-to-address-zero.patch mm-mseal-remove-further-superfluous-comments-do_mseal.patch mm-vma-introduce-vma-virtual-page-offset-field-and-add-helpers.patch mm-introduce-linear_virt_page_index.patch mm-abstract-vma_address-and-introduce-vma_anon_address.patch mm-update-print_bad_page_map-to-show-virtual-page-index.patch mm-introduce-and-use-vma_filebacked_address.patch mm-propagate-vma-virtual-page-offset-on-map-remap-split-merge.patch mm-rmap-track-whether-the-page-vma-mapped-walk-is-anonymous.patch mm-introduce-and-use-linear_folio_page_index.patch mm-rmap-use-virt-pgoff-for-map_private-file-backed-anon-folios.patch tools-testing-vma-expand-vma-merge-tests-to-assert-virt-pgoff.patch tools-testing-selftests-mm-test-virtual-page-offset-merge-behaviour.patch mm-vma-only-permit-map_private-dev-zero-to-be-mapped-anonymous.patch mm-vma-make-map_private-mapped-dev-zero-mappings-truly-anonymous.patch tools-testing-vma-add-test-to-assert-map_private-dev-zero-is-anon.patch tools-testing-selftests-mm-add-map_private-dev-zero-merge-tests.patch mm-huge_memory-separate-out-config_persistent_huge_zero_folio-logic.patch mm-huge_memory-fix-huge_zero_pfn-race.patch