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FAILED: patch "[PATCH] iommu/amd/pgtbl: Fix possible race while increase page table" failed to apply to 5.15-stable tree

by gregkh＠linuxfoundation.org

The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable(a)vger.kernel.org>. To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y git checkout FETCH_HEAD git cherry-pick -x 1e56310b40fd2e7e0b9493da9ff488af145bdd0c # <resolve conflicts, build, test, etc.> git commit -s git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2025092103-skilled-expand-23a8@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ From 1e56310b40fd2e7e0b9493da9ff488af145bdd0c Mon Sep 17 00:00:00 2001 From: Vasant Hegde <vasant.hegde(a)amd.com> Date: Sat, 13 Sep 2025 06:26:57 +0000 Subject: [PATCH] iommu/amd/pgtbl: Fix possible race while increase page table level The AMD IOMMU host page table implementation supports dynamic page table levels (up to 6 levels), starting with a 3-level configuration that expands based on IOVA address. The kernel maintains a root pointer and current page table level to enable proper page table walks in alloc_pte()/fetch_pte() operations. The IOMMU IOVA allocator initially starts with 32-bit address and onces its exhuasted it switches to 64-bit address (max address is determined based on IOMMU and device DMA capability). To support larger IOVA, AMD IOMMU driver increases page table level. But in unmap path (iommu_v1_unmap_pages()), fetch_pte() reads pgtable->[root/mode] without lock. So its possible that in exteme corner case, when increase_address_space() is updating pgtable->[root/mode], fetch_pte() reads wrong page table level (pgtable->mode). It does compare the value with level encoded in page table and returns NULL. This will result is iommu_unmap ops to fail and upper layer may retry/log WARN_ON. CPU 0 CPU 1 ------ ------ map pages unmap pages alloc_pte() -> increase_address_space() iommu_v1_unmap_pages() -> fetch_pte() pgtable->root = pte (new root value) READ pgtable->[mode/root] Reads new root, old mode Updates mode (pgtable->mode += 1) Since Page table level updates are infrequent and already synchronized with a spinlock, implement seqcount to enable lock-free read operations on the read path. Fixes: 754265bcab7 ("iommu/amd: Fix race in increase_address_space()") Reported-by: Alejandro Jimenez <alejandro.j.jimenez(a)oracle.com> Cc: stable(a)vger.kernel.org Cc: Joao Martins <joao.m.martins(a)oracle.com> Cc: Suravee Suthikulpanit <suravee.suthikulpanit(a)amd.com> Signed-off-by: Vasant Hegde <vasant.hegde(a)amd.com> Signed-off-by: Joerg Roedel <joerg.roedel(a)amd.com> diff --git a/drivers/iommu/amd/amd_iommu_types.h b/drivers/iommu/amd/amd_iommu_types.h index 5219d7ddfdaa..95f63c5f6159 100644 --- a/drivers/iommu/amd/amd_iommu_types.h +++ b/drivers/iommu/amd/amd_iommu_types.h @@ -555,6 +555,7 @@ struct gcr3_tbl_info { }; struct amd_io_pgtable { + seqcount_t seqcount; /* Protects root/mode update */ struct io_pgtable pgtbl; int mode; u64 *root; diff --git a/drivers/iommu/amd/io_pgtable.c b/drivers/iommu/amd/io_pgtable.c index a91e71f981ef..70c2f5b1631b 100644 --- a/drivers/iommu/amd/io_pgtable.c +++ b/drivers/iommu/amd/io_pgtable.c @@ -17,6 +17,7 @@ #include <linux/slab.h> #include <linux/types.h> #include <linux/dma-mapping.h> +#include <linux/seqlock.h> #include <asm/barrier.h> @@ -130,8 +131,11 @@ static bool increase_address_space(struct amd_io_pgtable *pgtable, *pte = PM_LEVEL_PDE(pgtable->mode, iommu_virt_to_phys(pgtable->root)); + write_seqcount_begin(&pgtable->seqcount); pgtable->root = pte; pgtable->mode += 1; + write_seqcount_end(&pgtable->seqcount); + amd_iommu_update_and_flush_device_table(domain); pte = NULL; @@ -153,6 +157,7 @@ static u64 *alloc_pte(struct amd_io_pgtable *pgtable, { unsigned long last_addr = address + (page_size - 1); struct io_pgtable_cfg *cfg = &pgtable->pgtbl.cfg; + unsigned int seqcount; int level, end_lvl; u64 *pte, *page; @@ -170,8 +175,14 @@ static u64 *alloc_pte(struct amd_io_pgtable *pgtable, } - level = pgtable->mode - 1; - pte = &pgtable->root[PM_LEVEL_INDEX(level, address)]; + do { + seqcount = read_seqcount_begin(&pgtable->seqcount); + + level = pgtable->mode - 1; + pte = &pgtable->root[PM_LEVEL_INDEX(level, address)]; + } while (read_seqcount_retry(&pgtable->seqcount, seqcount)); + + address = PAGE_SIZE_ALIGN(address, page_size); end_lvl = PAGE_SIZE_LEVEL(page_size); @@ -249,6 +260,7 @@ static u64 *fetch_pte(struct amd_io_pgtable *pgtable, unsigned long *page_size) { int level; + unsigned int seqcount; u64 *pte; *page_size = 0; @@ -256,8 +268,12 @@ static u64 *fetch_pte(struct amd_io_pgtable *pgtable, if (address > PM_LEVEL_SIZE(pgtable->mode)) return NULL; - level = pgtable->mode - 1; - pte = &pgtable->root[PM_LEVEL_INDEX(level, address)]; + do { + seqcount = read_seqcount_begin(&pgtable->seqcount); + level = pgtable->mode - 1; + pte = &pgtable->root[PM_LEVEL_INDEX(level, address)]; + } while (read_seqcount_retry(&pgtable->seqcount, seqcount)); + *page_size = PTE_LEVEL_PAGE_SIZE(level); while (level > 0) { @@ -541,6 +557,7 @@ static struct io_pgtable *v1_alloc_pgtable(struct io_pgtable_cfg *cfg, void *coo if (!pgtable->root) return NULL; pgtable->mode = PAGE_MODE_3_LEVEL; + seqcount_init(&pgtable->seqcount); cfg->pgsize_bitmap = amd_iommu_pgsize_bitmap; cfg->ias = IOMMU_IN_ADDR_BIT_SIZE;

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FAILED: patch "[PATCH] iommu/amd/pgtbl: Fix possible race while increase page table" failed to apply to 6.1-stable tree

by gregkh＠linuxfoundation.org

The patch below does not apply to the 6.1-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable(a)vger.kernel.org>. To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y git checkout FETCH_HEAD git cherry-pick -x 1e56310b40fd2e7e0b9493da9ff488af145bdd0c # <resolve conflicts, build, test, etc.> git commit -s git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2025092102-landfill-panorama-3049@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ From 1e56310b40fd2e7e0b9493da9ff488af145bdd0c Mon Sep 17 00:00:00 2001 From: Vasant Hegde <vasant.hegde(a)amd.com> Date: Sat, 13 Sep 2025 06:26:57 +0000 Subject: [PATCH] iommu/amd/pgtbl: Fix possible race while increase page table level The AMD IOMMU host page table implementation supports dynamic page table levels (up to 6 levels), starting with a 3-level configuration that expands based on IOVA address. The kernel maintains a root pointer and current page table level to enable proper page table walks in alloc_pte()/fetch_pte() operations. The IOMMU IOVA allocator initially starts with 32-bit address and onces its exhuasted it switches to 64-bit address (max address is determined based on IOMMU and device DMA capability). To support larger IOVA, AMD IOMMU driver increases page table level. But in unmap path (iommu_v1_unmap_pages()), fetch_pte() reads pgtable->[root/mode] without lock. So its possible that in exteme corner case, when increase_address_space() is updating pgtable->[root/mode], fetch_pte() reads wrong page table level (pgtable->mode). It does compare the value with level encoded in page table and returns NULL. This will result is iommu_unmap ops to fail and upper layer may retry/log WARN_ON. CPU 0 CPU 1 ------ ------ map pages unmap pages alloc_pte() -> increase_address_space() iommu_v1_unmap_pages() -> fetch_pte() pgtable->root = pte (new root value) READ pgtable->[mode/root] Reads new root, old mode Updates mode (pgtable->mode += 1) Since Page table level updates are infrequent and already synchronized with a spinlock, implement seqcount to enable lock-free read operations on the read path. Fixes: 754265bcab7 ("iommu/amd: Fix race in increase_address_space()") Reported-by: Alejandro Jimenez <alejandro.j.jimenez(a)oracle.com> Cc: stable(a)vger.kernel.org Cc: Joao Martins <joao.m.martins(a)oracle.com> Cc: Suravee Suthikulpanit <suravee.suthikulpanit(a)amd.com> Signed-off-by: Vasant Hegde <vasant.hegde(a)amd.com> Signed-off-by: Joerg Roedel <joerg.roedel(a)amd.com> diff --git a/drivers/iommu/amd/amd_iommu_types.h b/drivers/iommu/amd/amd_iommu_types.h index 5219d7ddfdaa..95f63c5f6159 100644 --- a/drivers/iommu/amd/amd_iommu_types.h +++ b/drivers/iommu/amd/amd_iommu_types.h @@ -555,6 +555,7 @@ struct gcr3_tbl_info { }; struct amd_io_pgtable { + seqcount_t seqcount; /* Protects root/mode update */ struct io_pgtable pgtbl; int mode; u64 *root; diff --git a/drivers/iommu/amd/io_pgtable.c b/drivers/iommu/amd/io_pgtable.c index a91e71f981ef..70c2f5b1631b 100644 --- a/drivers/iommu/amd/io_pgtable.c +++ b/drivers/iommu/amd/io_pgtable.c @@ -17,6 +17,7 @@ #include <linux/slab.h> #include <linux/types.h> #include <linux/dma-mapping.h> +#include <linux/seqlock.h> #include <asm/barrier.h> @@ -130,8 +131,11 @@ static bool increase_address_space(struct amd_io_pgtable *pgtable, *pte = PM_LEVEL_PDE(pgtable->mode, iommu_virt_to_phys(pgtable->root)); + write_seqcount_begin(&pgtable->seqcount); pgtable->root = pte; pgtable->mode += 1; + write_seqcount_end(&pgtable->seqcount); + amd_iommu_update_and_flush_device_table(domain); pte = NULL; @@ -153,6 +157,7 @@ static u64 *alloc_pte(struct amd_io_pgtable *pgtable, { unsigned long last_addr = address + (page_size - 1); struct io_pgtable_cfg *cfg = &pgtable->pgtbl.cfg; + unsigned int seqcount; int level, end_lvl; u64 *pte, *page; @@ -170,8 +175,14 @@ static u64 *alloc_pte(struct amd_io_pgtable *pgtable, } - level = pgtable->mode - 1; - pte = &pgtable->root[PM_LEVEL_INDEX(level, address)]; + do { + seqcount = read_seqcount_begin(&pgtable->seqcount); + + level = pgtable->mode - 1; + pte = &pgtable->root[PM_LEVEL_INDEX(level, address)]; + } while (read_seqcount_retry(&pgtable->seqcount, seqcount)); + + address = PAGE_SIZE_ALIGN(address, page_size); end_lvl = PAGE_SIZE_LEVEL(page_size); @@ -249,6 +260,7 @@ static u64 *fetch_pte(struct amd_io_pgtable *pgtable, unsigned long *page_size) { int level; + unsigned int seqcount; u64 *pte; *page_size = 0; @@ -256,8 +268,12 @@ static u64 *fetch_pte(struct amd_io_pgtable *pgtable, if (address > PM_LEVEL_SIZE(pgtable->mode)) return NULL; - level = pgtable->mode - 1; - pte = &pgtable->root[PM_LEVEL_INDEX(level, address)]; + do { + seqcount = read_seqcount_begin(&pgtable->seqcount); + level = pgtable->mode - 1; + pte = &pgtable->root[PM_LEVEL_INDEX(level, address)]; + } while (read_seqcount_retry(&pgtable->seqcount, seqcount)); + *page_size = PTE_LEVEL_PAGE_SIZE(level); while (level > 0) { @@ -541,6 +557,7 @@ static struct io_pgtable *v1_alloc_pgtable(struct io_pgtable_cfg *cfg, void *coo if (!pgtable->root) return NULL; pgtable->mode = PAGE_MODE_3_LEVEL; + seqcount_init(&pgtable->seqcount); cfg->pgsize_bitmap = amd_iommu_pgsize_bitmap; cfg->ias = IOMMU_IN_ADDR_BIT_SIZE;

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FAILED: patch "[PATCH] samples/damon/prcl: avoid starting DAMON before" failed to apply to 6.16-stable tree

by gregkh＠linuxfoundation.org

The patch below does not apply to the 6.16-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable(a)vger.kernel.org>. To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.16.y git checkout FETCH_HEAD git cherry-pick -x e6b733ca2f99e968d696c2e812c8eb8e090bf37b # <resolve conflicts, build, test, etc.> git commit -s git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2025092121-boned-marbles-55ea@gregkh' --subject-prefix 'PATCH 6.16.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ From e6b733ca2f99e968d696c2e812c8eb8e090bf37b Mon Sep 17 00:00:00 2001 From: SeongJae Park <sj(a)kernel.org> Date: Mon, 8 Sep 2025 19:22:37 -0700 Subject: [PATCH] samples/damon/prcl: avoid starting DAMON before initialization Commit 2780505ec2b4 ("samples/damon/prcl: fix boot time enable crash") is somehow incompletely applying the origin patch [1]. It is missing the part that avoids starting DAMON before module initialization. Probably a mistake during a merge has happened. Fix it by applying the missed part again. Link: https://lkml.kernel.org/r/20250909022238.2989-3-sj@kernel.org Link: https://lore.kernel.org/20250706193207.39810-3-sj@kernel.org [1] Fixes: 2780505ec2b4 ("samples/damon/prcl: fix boot time enable crash") Signed-off-by: SeongJae Park <sj(a)kernel.org> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> diff --git a/samples/damon/prcl.c b/samples/damon/prcl.c index 1b839c06a612..0226652f94d5 100644 --- a/samples/damon/prcl.c +++ b/samples/damon/prcl.c @@ -137,6 +137,9 @@ static int damon_sample_prcl_enable_store( if (enabled == is_enabled) return 0; + if (!init_called) + return 0; + if (enabled) { err = damon_sample_prcl_start(); if (err)

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FAILED: patch "[PATCH] mm: folio_may_be_lru_cached() unless folio_test_large()" failed to apply to 5.4-stable tree

by gregkh＠linuxfoundation.org

The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable(a)vger.kernel.org>. To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.4.y git checkout FETCH_HEAD git cherry-pick -x 2da6de30e60dd9bb14600eff1cc99df2fa2ddae3 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2025092147-truck-ceremony-311d@gregkh' --subject-prefix 'PATCH 5.4.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ From 2da6de30e60dd9bb14600eff1cc99df2fa2ddae3 Mon Sep 17 00:00:00 2001 From: Hugh Dickins <hughd(a)google.com> Date: Mon, 8 Sep 2025 15:23:15 -0700 Subject: [PATCH] mm: folio_may_be_lru_cached() unless folio_test_large() mm/swap.c and mm/mlock.c agree to drain any per-CPU batch as soon as a large folio is added: so collect_longterm_unpinnable_folios() just wastes effort when calling lru_add_drain[_all]() on a large folio. But although there is good reason not to batch up PMD-sized folios, we might well benefit from batching a small number of low-order mTHPs (though unclear how that "small number" limitation will be implemented). So ask if folio_may_be_lru_cached() rather than !folio_test_large(), to insulate those particular checks from future change. Name preferred to "folio_is_batchable" because large folios can well be put on a batch: it's just the per-CPU LRU caches, drained much later, which need care. Marked for stable, to counter the increase in lru_add_drain_all()s from "mm/gup: check ref_count instead of lru before migration". Link: https://lkml.kernel.org/r/57d2eaf8-3607-f318-e0c5-be02dce61ad0@google.com Fixes: 9a4e9f3b2d73 ("mm: update get_user_pages_longterm to migrate pages allocated from CMA region") Signed-off-by: Hugh Dickins <hughd(a)google.com> Suggested-by: David Hildenbrand <david(a)redhat.com> Acked-by: David Hildenbrand <david(a)redhat.com> Cc: "Aneesh Kumar K.V" <aneesh.kumar(a)kernel.org> Cc: Axel Rasmussen <axelrasmussen(a)google.com> Cc: Chris Li <chrisl(a)kernel.org> Cc: Christoph Hellwig <hch(a)infradead.org> Cc: Jason Gunthorpe <jgg(a)ziepe.ca> Cc: Johannes Weiner <hannes(a)cmpxchg.org> Cc: John Hubbard <jhubbard(a)nvidia.com> Cc: Keir Fraser <keirf(a)google.com> Cc: Konstantin Khlebnikov <koct9i(a)gmail.com> Cc: Li Zhe <lizhe.67(a)bytedance.com> Cc: Matthew Wilcox (Oracle) <willy(a)infradead.org> Cc: Peter Xu <peterx(a)redhat.com> Cc: Rik van Riel <riel(a)surriel.com> Cc: Shivank Garg <shivankg(a)amd.com> Cc: Vlastimil Babka <vbabka(a)suse.cz> Cc: Wei Xu <weixugc(a)google.com> Cc: Will Deacon <will(a)kernel.org> Cc: yangge <yangge1116(a)126.com> Cc: Yuanchu Xie <yuanchu(a)google.com> Cc: Yu Zhao <yuzhao(a)google.com> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> diff --git a/include/linux/swap.h b/include/linux/swap.h index 2fe6ed2cc3fd..7012a0f758d8 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -385,6 +385,16 @@ void folio_add_lru_vma(struct folio *, struct vm_area_struct *); void mark_page_accessed(struct page *); void folio_mark_accessed(struct folio *); +static inline bool folio_may_be_lru_cached(struct folio *folio) +{ + /* + * Holding PMD-sized folios in per-CPU LRU cache unbalances accounting. + * Holding small numbers of low-order mTHP folios in per-CPU LRU cache + * will be sensible, but nobody has implemented and tested that yet. + */ + return !folio_test_large(folio); +} + extern atomic_t lru_disable_count; static inline bool lru_cache_disabled(void) diff --git a/mm/gup.c b/mm/gup.c index b47066a54f52..0bc4d140fc07 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2307,13 +2307,13 @@ static unsigned long collect_longterm_unpinnable_folios( continue; } - if (drained == 0 && + if (drained == 0 && folio_may_be_lru_cached(folio) && folio_ref_count(folio) != folio_expected_ref_count(folio) + 1) { lru_add_drain(); drained = 1; } - if (drained == 1 && + if (drained == 1 && folio_may_be_lru_cached(folio) && folio_ref_count(folio) != folio_expected_ref_count(folio) + 1) { lru_add_drain_all(); diff --git a/mm/mlock.c b/mm/mlock.c index a1d93ad33c6d..bb0776f5ef7c 100644 --- a/mm/mlock.c +++ b/mm/mlock.c @@ -255,7 +255,7 @@ void mlock_folio(struct folio *folio) folio_get(folio); if (!folio_batch_add(fbatch, mlock_lru(folio)) || - folio_test_large(folio) || lru_cache_disabled()) + !folio_may_be_lru_cached(folio) || lru_cache_disabled()) mlock_folio_batch(fbatch); local_unlock(&mlock_fbatch.lock); } @@ -278,7 +278,7 @@ void mlock_new_folio(struct folio *folio) folio_get(folio); if (!folio_batch_add(fbatch, mlock_new(folio)) || - folio_test_large(folio) || lru_cache_disabled()) + !folio_may_be_lru_cached(folio) || lru_cache_disabled()) mlock_folio_batch(fbatch); local_unlock(&mlock_fbatch.lock); } @@ -299,7 +299,7 @@ void munlock_folio(struct folio *folio) */ folio_get(folio); if (!folio_batch_add(fbatch, folio) || - folio_test_large(folio) || lru_cache_disabled()) + !folio_may_be_lru_cached(folio) || lru_cache_disabled()) mlock_folio_batch(fbatch); local_unlock(&mlock_fbatch.lock); } diff --git a/mm/swap.c b/mm/swap.c index 6ae2d5680574..b74ebe865dd9 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -192,7 +192,7 @@ static void __folio_batch_add_and_move(struct folio_batch __percpu *fbatch, local_lock(&cpu_fbatches.lock); if (!folio_batch_add(this_cpu_ptr(fbatch), folio) || - folio_test_large(folio) || lru_cache_disabled()) + !folio_may_be_lru_cached(folio) || lru_cache_disabled()) folio_batch_move_lru(this_cpu_ptr(fbatch), move_fn); if (disable_irq)

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FAILED: patch "[PATCH] mm: folio_may_be_lru_cached() unless folio_test_large()" failed to apply to 5.10-stable tree

by gregkh＠linuxfoundation.org

The patch below does not apply to the 5.10-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable(a)vger.kernel.org>. To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y git checkout FETCH_HEAD git cherry-pick -x 2da6de30e60dd9bb14600eff1cc99df2fa2ddae3 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2025092146-exhume-krypton-1383@gregkh' --subject-prefix 'PATCH 5.10.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ From 2da6de30e60dd9bb14600eff1cc99df2fa2ddae3 Mon Sep 17 00:00:00 2001 From: Hugh Dickins <hughd(a)google.com> Date: Mon, 8 Sep 2025 15:23:15 -0700 Subject: [PATCH] mm: folio_may_be_lru_cached() unless folio_test_large() mm/swap.c and mm/mlock.c agree to drain any per-CPU batch as soon as a large folio is added: so collect_longterm_unpinnable_folios() just wastes effort when calling lru_add_drain[_all]() on a large folio. But although there is good reason not to batch up PMD-sized folios, we might well benefit from batching a small number of low-order mTHPs (though unclear how that "small number" limitation will be implemented). So ask if folio_may_be_lru_cached() rather than !folio_test_large(), to insulate those particular checks from future change. Name preferred to "folio_is_batchable" because large folios can well be put on a batch: it's just the per-CPU LRU caches, drained much later, which need care. Marked for stable, to counter the increase in lru_add_drain_all()s from "mm/gup: check ref_count instead of lru before migration". Link: https://lkml.kernel.org/r/57d2eaf8-3607-f318-e0c5-be02dce61ad0@google.com Fixes: 9a4e9f3b2d73 ("mm: update get_user_pages_longterm to migrate pages allocated from CMA region") Signed-off-by: Hugh Dickins <hughd(a)google.com> Suggested-by: David Hildenbrand <david(a)redhat.com> Acked-by: David Hildenbrand <david(a)redhat.com> Cc: "Aneesh Kumar K.V" <aneesh.kumar(a)kernel.org> Cc: Axel Rasmussen <axelrasmussen(a)google.com> Cc: Chris Li <chrisl(a)kernel.org> Cc: Christoph Hellwig <hch(a)infradead.org> Cc: Jason Gunthorpe <jgg(a)ziepe.ca> Cc: Johannes Weiner <hannes(a)cmpxchg.org> Cc: John Hubbard <jhubbard(a)nvidia.com> Cc: Keir Fraser <keirf(a)google.com> Cc: Konstantin Khlebnikov <koct9i(a)gmail.com> Cc: Li Zhe <lizhe.67(a)bytedance.com> Cc: Matthew Wilcox (Oracle) <willy(a)infradead.org> Cc: Peter Xu <peterx(a)redhat.com> Cc: Rik van Riel <riel(a)surriel.com> Cc: Shivank Garg <shivankg(a)amd.com> Cc: Vlastimil Babka <vbabka(a)suse.cz> Cc: Wei Xu <weixugc(a)google.com> Cc: Will Deacon <will(a)kernel.org> Cc: yangge <yangge1116(a)126.com> Cc: Yuanchu Xie <yuanchu(a)google.com> Cc: Yu Zhao <yuzhao(a)google.com> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> diff --git a/include/linux/swap.h b/include/linux/swap.h index 2fe6ed2cc3fd..7012a0f758d8 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -385,6 +385,16 @@ void folio_add_lru_vma(struct folio *, struct vm_area_struct *); void mark_page_accessed(struct page *); void folio_mark_accessed(struct folio *); +static inline bool folio_may_be_lru_cached(struct folio *folio) +{ + /* + * Holding PMD-sized folios in per-CPU LRU cache unbalances accounting. + * Holding small numbers of low-order mTHP folios in per-CPU LRU cache + * will be sensible, but nobody has implemented and tested that yet. + */ + return !folio_test_large(folio); +} + extern atomic_t lru_disable_count; static inline bool lru_cache_disabled(void) diff --git a/mm/gup.c b/mm/gup.c index b47066a54f52..0bc4d140fc07 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2307,13 +2307,13 @@ static unsigned long collect_longterm_unpinnable_folios( continue; } - if (drained == 0 && + if (drained == 0 && folio_may_be_lru_cached(folio) && folio_ref_count(folio) != folio_expected_ref_count(folio) + 1) { lru_add_drain(); drained = 1; } - if (drained == 1 && + if (drained == 1 && folio_may_be_lru_cached(folio) && folio_ref_count(folio) != folio_expected_ref_count(folio) + 1) { lru_add_drain_all(); diff --git a/mm/mlock.c b/mm/mlock.c index a1d93ad33c6d..bb0776f5ef7c 100644 --- a/mm/mlock.c +++ b/mm/mlock.c @@ -255,7 +255,7 @@ void mlock_folio(struct folio *folio) folio_get(folio); if (!folio_batch_add(fbatch, mlock_lru(folio)) || - folio_test_large(folio) || lru_cache_disabled()) + !folio_may_be_lru_cached(folio) || lru_cache_disabled()) mlock_folio_batch(fbatch); local_unlock(&mlock_fbatch.lock); } @@ -278,7 +278,7 @@ void mlock_new_folio(struct folio *folio) folio_get(folio); if (!folio_batch_add(fbatch, mlock_new(folio)) || - folio_test_large(folio) || lru_cache_disabled()) + !folio_may_be_lru_cached(folio) || lru_cache_disabled()) mlock_folio_batch(fbatch); local_unlock(&mlock_fbatch.lock); } @@ -299,7 +299,7 @@ void munlock_folio(struct folio *folio) */ folio_get(folio); if (!folio_batch_add(fbatch, folio) || - folio_test_large(folio) || lru_cache_disabled()) + !folio_may_be_lru_cached(folio) || lru_cache_disabled()) mlock_folio_batch(fbatch); local_unlock(&mlock_fbatch.lock); } diff --git a/mm/swap.c b/mm/swap.c index 6ae2d5680574..b74ebe865dd9 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -192,7 +192,7 @@ static void __folio_batch_add_and_move(struct folio_batch __percpu *fbatch, local_lock(&cpu_fbatches.lock); if (!folio_batch_add(this_cpu_ptr(fbatch), folio) || - folio_test_large(folio) || lru_cache_disabled()) + !folio_may_be_lru_cached(folio) || lru_cache_disabled()) folio_batch_move_lru(this_cpu_ptr(fbatch), move_fn); if (disable_irq)

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FAILED: patch "[PATCH] mm: folio_may_be_lru_cached() unless folio_test_large()" failed to apply to 5.15-stable tree

by gregkh＠linuxfoundation.org

The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable(a)vger.kernel.org>. To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y git checkout FETCH_HEAD git cherry-pick -x 2da6de30e60dd9bb14600eff1cc99df2fa2ddae3 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2025092145-system-superjet-a0fb@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ From 2da6de30e60dd9bb14600eff1cc99df2fa2ddae3 Mon Sep 17 00:00:00 2001 From: Hugh Dickins <hughd(a)google.com> Date: Mon, 8 Sep 2025 15:23:15 -0700 Subject: [PATCH] mm: folio_may_be_lru_cached() unless folio_test_large() mm/swap.c and mm/mlock.c agree to drain any per-CPU batch as soon as a large folio is added: so collect_longterm_unpinnable_folios() just wastes effort when calling lru_add_drain[_all]() on a large folio. But although there is good reason not to batch up PMD-sized folios, we might well benefit from batching a small number of low-order mTHPs (though unclear how that "small number" limitation will be implemented). So ask if folio_may_be_lru_cached() rather than !folio_test_large(), to insulate those particular checks from future change. Name preferred to "folio_is_batchable" because large folios can well be put on a batch: it's just the per-CPU LRU caches, drained much later, which need care. Marked for stable, to counter the increase in lru_add_drain_all()s from "mm/gup: check ref_count instead of lru before migration". Link: https://lkml.kernel.org/r/57d2eaf8-3607-f318-e0c5-be02dce61ad0@google.com Fixes: 9a4e9f3b2d73 ("mm: update get_user_pages_longterm to migrate pages allocated from CMA region") Signed-off-by: Hugh Dickins <hughd(a)google.com> Suggested-by: David Hildenbrand <david(a)redhat.com> Acked-by: David Hildenbrand <david(a)redhat.com> Cc: "Aneesh Kumar K.V" <aneesh.kumar(a)kernel.org> Cc: Axel Rasmussen <axelrasmussen(a)google.com> Cc: Chris Li <chrisl(a)kernel.org> Cc: Christoph Hellwig <hch(a)infradead.org> Cc: Jason Gunthorpe <jgg(a)ziepe.ca> Cc: Johannes Weiner <hannes(a)cmpxchg.org> Cc: John Hubbard <jhubbard(a)nvidia.com> Cc: Keir Fraser <keirf(a)google.com> Cc: Konstantin Khlebnikov <koct9i(a)gmail.com> Cc: Li Zhe <lizhe.67(a)bytedance.com> Cc: Matthew Wilcox (Oracle) <willy(a)infradead.org> Cc: Peter Xu <peterx(a)redhat.com> Cc: Rik van Riel <riel(a)surriel.com> Cc: Shivank Garg <shivankg(a)amd.com> Cc: Vlastimil Babka <vbabka(a)suse.cz> Cc: Wei Xu <weixugc(a)google.com> Cc: Will Deacon <will(a)kernel.org> Cc: yangge <yangge1116(a)126.com> Cc: Yuanchu Xie <yuanchu(a)google.com> Cc: Yu Zhao <yuzhao(a)google.com> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> diff --git a/include/linux/swap.h b/include/linux/swap.h index 2fe6ed2cc3fd..7012a0f758d8 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -385,6 +385,16 @@ void folio_add_lru_vma(struct folio *, struct vm_area_struct *); void mark_page_accessed(struct page *); void folio_mark_accessed(struct folio *); +static inline bool folio_may_be_lru_cached(struct folio *folio) +{ + /* + * Holding PMD-sized folios in per-CPU LRU cache unbalances accounting. + * Holding small numbers of low-order mTHP folios in per-CPU LRU cache + * will be sensible, but nobody has implemented and tested that yet. + */ + return !folio_test_large(folio); +} + extern atomic_t lru_disable_count; static inline bool lru_cache_disabled(void) diff --git a/mm/gup.c b/mm/gup.c index b47066a54f52..0bc4d140fc07 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2307,13 +2307,13 @@ static unsigned long collect_longterm_unpinnable_folios( continue; } - if (drained == 0 && + if (drained == 0 && folio_may_be_lru_cached(folio) && folio_ref_count(folio) != folio_expected_ref_count(folio) + 1) { lru_add_drain(); drained = 1; } - if (drained == 1 && + if (drained == 1 && folio_may_be_lru_cached(folio) && folio_ref_count(folio) != folio_expected_ref_count(folio) + 1) { lru_add_drain_all(); diff --git a/mm/mlock.c b/mm/mlock.c index a1d93ad33c6d..bb0776f5ef7c 100644 --- a/mm/mlock.c +++ b/mm/mlock.c @@ -255,7 +255,7 @@ void mlock_folio(struct folio *folio) folio_get(folio); if (!folio_batch_add(fbatch, mlock_lru(folio)) || - folio_test_large(folio) || lru_cache_disabled()) + !folio_may_be_lru_cached(folio) || lru_cache_disabled()) mlock_folio_batch(fbatch); local_unlock(&mlock_fbatch.lock); } @@ -278,7 +278,7 @@ void mlock_new_folio(struct folio *folio) folio_get(folio); if (!folio_batch_add(fbatch, mlock_new(folio)) || - folio_test_large(folio) || lru_cache_disabled()) + !folio_may_be_lru_cached(folio) || lru_cache_disabled()) mlock_folio_batch(fbatch); local_unlock(&mlock_fbatch.lock); } @@ -299,7 +299,7 @@ void munlock_folio(struct folio *folio) */ folio_get(folio); if (!folio_batch_add(fbatch, folio) || - folio_test_large(folio) || lru_cache_disabled()) + !folio_may_be_lru_cached(folio) || lru_cache_disabled()) mlock_folio_batch(fbatch); local_unlock(&mlock_fbatch.lock); } diff --git a/mm/swap.c b/mm/swap.c index 6ae2d5680574..b74ebe865dd9 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -192,7 +192,7 @@ static void __folio_batch_add_and_move(struct folio_batch __percpu *fbatch, local_lock(&cpu_fbatches.lock); if (!folio_batch_add(this_cpu_ptr(fbatch), folio) || - folio_test_large(folio) || lru_cache_disabled()) + !folio_may_be_lru_cached(folio) || lru_cache_disabled()) folio_batch_move_lru(this_cpu_ptr(fbatch), move_fn); if (disable_irq)

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FAILED: patch "[PATCH] mm: folio_may_be_lru_cached() unless folio_test_large()" failed to apply to 6.1-stable tree

by gregkh＠linuxfoundation.org

The patch below does not apply to the 6.1-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable(a)vger.kernel.org>. To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y git checkout FETCH_HEAD git cherry-pick -x 2da6de30e60dd9bb14600eff1cc99df2fa2ddae3 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2025092144-angler-cuddly-30db@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ From 2da6de30e60dd9bb14600eff1cc99df2fa2ddae3 Mon Sep 17 00:00:00 2001 From: Hugh Dickins <hughd(a)google.com> Date: Mon, 8 Sep 2025 15:23:15 -0700 Subject: [PATCH] mm: folio_may_be_lru_cached() unless folio_test_large() mm/swap.c and mm/mlock.c agree to drain any per-CPU batch as soon as a large folio is added: so collect_longterm_unpinnable_folios() just wastes effort when calling lru_add_drain[_all]() on a large folio. But although there is good reason not to batch up PMD-sized folios, we might well benefit from batching a small number of low-order mTHPs (though unclear how that "small number" limitation will be implemented). So ask if folio_may_be_lru_cached() rather than !folio_test_large(), to insulate those particular checks from future change. Name preferred to "folio_is_batchable" because large folios can well be put on a batch: it's just the per-CPU LRU caches, drained much later, which need care. Marked for stable, to counter the increase in lru_add_drain_all()s from "mm/gup: check ref_count instead of lru before migration". Link: https://lkml.kernel.org/r/57d2eaf8-3607-f318-e0c5-be02dce61ad0@google.com Fixes: 9a4e9f3b2d73 ("mm: update get_user_pages_longterm to migrate pages allocated from CMA region") Signed-off-by: Hugh Dickins <hughd(a)google.com> Suggested-by: David Hildenbrand <david(a)redhat.com> Acked-by: David Hildenbrand <david(a)redhat.com> Cc: "Aneesh Kumar K.V" <aneesh.kumar(a)kernel.org> Cc: Axel Rasmussen <axelrasmussen(a)google.com> Cc: Chris Li <chrisl(a)kernel.org> Cc: Christoph Hellwig <hch(a)infradead.org> Cc: Jason Gunthorpe <jgg(a)ziepe.ca> Cc: Johannes Weiner <hannes(a)cmpxchg.org> Cc: John Hubbard <jhubbard(a)nvidia.com> Cc: Keir Fraser <keirf(a)google.com> Cc: Konstantin Khlebnikov <koct9i(a)gmail.com> Cc: Li Zhe <lizhe.67(a)bytedance.com> Cc: Matthew Wilcox (Oracle) <willy(a)infradead.org> Cc: Peter Xu <peterx(a)redhat.com> Cc: Rik van Riel <riel(a)surriel.com> Cc: Shivank Garg <shivankg(a)amd.com> Cc: Vlastimil Babka <vbabka(a)suse.cz> Cc: Wei Xu <weixugc(a)google.com> Cc: Will Deacon <will(a)kernel.org> Cc: yangge <yangge1116(a)126.com> Cc: Yuanchu Xie <yuanchu(a)google.com> Cc: Yu Zhao <yuzhao(a)google.com> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> diff --git a/include/linux/swap.h b/include/linux/swap.h index 2fe6ed2cc3fd..7012a0f758d8 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -385,6 +385,16 @@ void folio_add_lru_vma(struct folio *, struct vm_area_struct *); void mark_page_accessed(struct page *); void folio_mark_accessed(struct folio *); +static inline bool folio_may_be_lru_cached(struct folio *folio) +{ + /* + * Holding PMD-sized folios in per-CPU LRU cache unbalances accounting. + * Holding small numbers of low-order mTHP folios in per-CPU LRU cache + * will be sensible, but nobody has implemented and tested that yet. + */ + return !folio_test_large(folio); +} + extern atomic_t lru_disable_count; static inline bool lru_cache_disabled(void) diff --git a/mm/gup.c b/mm/gup.c index b47066a54f52..0bc4d140fc07 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2307,13 +2307,13 @@ static unsigned long collect_longterm_unpinnable_folios( continue; } - if (drained == 0 && + if (drained == 0 && folio_may_be_lru_cached(folio) && folio_ref_count(folio) != folio_expected_ref_count(folio) + 1) { lru_add_drain(); drained = 1; } - if (drained == 1 && + if (drained == 1 && folio_may_be_lru_cached(folio) && folio_ref_count(folio) != folio_expected_ref_count(folio) + 1) { lru_add_drain_all(); diff --git a/mm/mlock.c b/mm/mlock.c index a1d93ad33c6d..bb0776f5ef7c 100644 --- a/mm/mlock.c +++ b/mm/mlock.c @@ -255,7 +255,7 @@ void mlock_folio(struct folio *folio) folio_get(folio); if (!folio_batch_add(fbatch, mlock_lru(folio)) || - folio_test_large(folio) || lru_cache_disabled()) + !folio_may_be_lru_cached(folio) || lru_cache_disabled()) mlock_folio_batch(fbatch); local_unlock(&mlock_fbatch.lock); } @@ -278,7 +278,7 @@ void mlock_new_folio(struct folio *folio) folio_get(folio); if (!folio_batch_add(fbatch, mlock_new(folio)) || - folio_test_large(folio) || lru_cache_disabled()) + !folio_may_be_lru_cached(folio) || lru_cache_disabled()) mlock_folio_batch(fbatch); local_unlock(&mlock_fbatch.lock); } @@ -299,7 +299,7 @@ void munlock_folio(struct folio *folio) */ folio_get(folio); if (!folio_batch_add(fbatch, folio) || - folio_test_large(folio) || lru_cache_disabled()) + !folio_may_be_lru_cached(folio) || lru_cache_disabled()) mlock_folio_batch(fbatch); local_unlock(&mlock_fbatch.lock); } diff --git a/mm/swap.c b/mm/swap.c index 6ae2d5680574..b74ebe865dd9 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -192,7 +192,7 @@ static void __folio_batch_add_and_move(struct folio_batch __percpu *fbatch, local_lock(&cpu_fbatches.lock); if (!folio_batch_add(this_cpu_ptr(fbatch), folio) || - folio_test_large(folio) || lru_cache_disabled()) + !folio_may_be_lru_cached(folio) || lru_cache_disabled()) folio_batch_move_lru(this_cpu_ptr(fbatch), move_fn); if (disable_irq)

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FAILED: patch "[PATCH] mm: folio_may_be_lru_cached() unless folio_test_large()" failed to apply to 6.6-stable tree

by gregkh＠linuxfoundation.org

The patch below does not apply to the 6.6-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable(a)vger.kernel.org>. To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y git checkout FETCH_HEAD git cherry-pick -x 2da6de30e60dd9bb14600eff1cc99df2fa2ddae3 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2025092143-defrost-backboned-d1ea@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ From 2da6de30e60dd9bb14600eff1cc99df2fa2ddae3 Mon Sep 17 00:00:00 2001 From: Hugh Dickins <hughd(a)google.com> Date: Mon, 8 Sep 2025 15:23:15 -0700 Subject: [PATCH] mm: folio_may_be_lru_cached() unless folio_test_large() mm/swap.c and mm/mlock.c agree to drain any per-CPU batch as soon as a large folio is added: so collect_longterm_unpinnable_folios() just wastes effort when calling lru_add_drain[_all]() on a large folio. But although there is good reason not to batch up PMD-sized folios, we might well benefit from batching a small number of low-order mTHPs (though unclear how that "small number" limitation will be implemented). So ask if folio_may_be_lru_cached() rather than !folio_test_large(), to insulate those particular checks from future change. Name preferred to "folio_is_batchable" because large folios can well be put on a batch: it's just the per-CPU LRU caches, drained much later, which need care. Marked for stable, to counter the increase in lru_add_drain_all()s from "mm/gup: check ref_count instead of lru before migration". Link: https://lkml.kernel.org/r/57d2eaf8-3607-f318-e0c5-be02dce61ad0@google.com Fixes: 9a4e9f3b2d73 ("mm: update get_user_pages_longterm to migrate pages allocated from CMA region") Signed-off-by: Hugh Dickins <hughd(a)google.com> Suggested-by: David Hildenbrand <david(a)redhat.com> Acked-by: David Hildenbrand <david(a)redhat.com> Cc: "Aneesh Kumar K.V" <aneesh.kumar(a)kernel.org> Cc: Axel Rasmussen <axelrasmussen(a)google.com> Cc: Chris Li <chrisl(a)kernel.org> Cc: Christoph Hellwig <hch(a)infradead.org> Cc: Jason Gunthorpe <jgg(a)ziepe.ca> Cc: Johannes Weiner <hannes(a)cmpxchg.org> Cc: John Hubbard <jhubbard(a)nvidia.com> Cc: Keir Fraser <keirf(a)google.com> Cc: Konstantin Khlebnikov <koct9i(a)gmail.com> Cc: Li Zhe <lizhe.67(a)bytedance.com> Cc: Matthew Wilcox (Oracle) <willy(a)infradead.org> Cc: Peter Xu <peterx(a)redhat.com> Cc: Rik van Riel <riel(a)surriel.com> Cc: Shivank Garg <shivankg(a)amd.com> Cc: Vlastimil Babka <vbabka(a)suse.cz> Cc: Wei Xu <weixugc(a)google.com> Cc: Will Deacon <will(a)kernel.org> Cc: yangge <yangge1116(a)126.com> Cc: Yuanchu Xie <yuanchu(a)google.com> Cc: Yu Zhao <yuzhao(a)google.com> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> diff --git a/include/linux/swap.h b/include/linux/swap.h index 2fe6ed2cc3fd..7012a0f758d8 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -385,6 +385,16 @@ void folio_add_lru_vma(struct folio *, struct vm_area_struct *); void mark_page_accessed(struct page *); void folio_mark_accessed(struct folio *); +static inline bool folio_may_be_lru_cached(struct folio *folio) +{ + /* + * Holding PMD-sized folios in per-CPU LRU cache unbalances accounting. + * Holding small numbers of low-order mTHP folios in per-CPU LRU cache + * will be sensible, but nobody has implemented and tested that yet. + */ + return !folio_test_large(folio); +} + extern atomic_t lru_disable_count; static inline bool lru_cache_disabled(void) diff --git a/mm/gup.c b/mm/gup.c index b47066a54f52..0bc4d140fc07 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2307,13 +2307,13 @@ static unsigned long collect_longterm_unpinnable_folios( continue; } - if (drained == 0 && + if (drained == 0 && folio_may_be_lru_cached(folio) && folio_ref_count(folio) != folio_expected_ref_count(folio) + 1) { lru_add_drain(); drained = 1; } - if (drained == 1 && + if (drained == 1 && folio_may_be_lru_cached(folio) && folio_ref_count(folio) != folio_expected_ref_count(folio) + 1) { lru_add_drain_all(); diff --git a/mm/mlock.c b/mm/mlock.c index a1d93ad33c6d..bb0776f5ef7c 100644 --- a/mm/mlock.c +++ b/mm/mlock.c @@ -255,7 +255,7 @@ void mlock_folio(struct folio *folio) folio_get(folio); if (!folio_batch_add(fbatch, mlock_lru(folio)) || - folio_test_large(folio) || lru_cache_disabled()) + !folio_may_be_lru_cached(folio) || lru_cache_disabled()) mlock_folio_batch(fbatch); local_unlock(&mlock_fbatch.lock); } @@ -278,7 +278,7 @@ void mlock_new_folio(struct folio *folio) folio_get(folio); if (!folio_batch_add(fbatch, mlock_new(folio)) || - folio_test_large(folio) || lru_cache_disabled()) + !folio_may_be_lru_cached(folio) || lru_cache_disabled()) mlock_folio_batch(fbatch); local_unlock(&mlock_fbatch.lock); } @@ -299,7 +299,7 @@ void munlock_folio(struct folio *folio) */ folio_get(folio); if (!folio_batch_add(fbatch, folio) || - folio_test_large(folio) || lru_cache_disabled()) + !folio_may_be_lru_cached(folio) || lru_cache_disabled()) mlock_folio_batch(fbatch); local_unlock(&mlock_fbatch.lock); } diff --git a/mm/swap.c b/mm/swap.c index 6ae2d5680574..b74ebe865dd9 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -192,7 +192,7 @@ static void __folio_batch_add_and_move(struct folio_batch __percpu *fbatch, local_lock(&cpu_fbatches.lock); if (!folio_batch_add(this_cpu_ptr(fbatch), folio) || - folio_test_large(folio) || lru_cache_disabled()) + !folio_may_be_lru_cached(folio) || lru_cache_disabled()) folio_batch_move_lru(this_cpu_ptr(fbatch), move_fn); if (disable_irq)

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FAILED: patch "[PATCH] mm/gup: check ref_count instead of lru before migration" failed to apply to 5.4-stable tree

by gregkh＠linuxfoundation.org

The patch below does not apply to the 5.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable(a)vger.kernel.org>. To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.4.y git checkout FETCH_HEAD git cherry-pick -x 98c6d259319ecf6e8d027abd3f14b81324b8c0ad # <resolve conflicts, build, test, etc.> git commit -s git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2025092156-candied-rogue-bf08@gregkh' --subject-prefix 'PATCH 5.4.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ From 98c6d259319ecf6e8d027abd3f14b81324b8c0ad Mon Sep 17 00:00:00 2001 From: Hugh Dickins <hughd(a)google.com> Date: Mon, 8 Sep 2025 15:15:03 -0700 Subject: [PATCH] mm/gup: check ref_count instead of lru before migration Patch series "mm: better GUP pin lru_add_drain_all()", v2. Series of lru_add_drain_all()-related patches, arising from recent mm/gup migration report from Will Deacon. This patch (of 5): Will Deacon reports:- When taking a longterm GUP pin via pin_user_pages(), __gup_longterm_locked() tries to migrate target folios that should not be longterm pinned, for example because they reside in a CMA region or movable zone. This is done by first pinning all of the target folios anyway, collecting all of the longterm-unpinnable target folios into a list, dropping the pins that were just taken and finally handing the list off to migrate_pages() for the actual migration. It is critically important that no unexpected references are held on the folios being migrated, otherwise the migration will fail and pin_user_pages() will return -ENOMEM to its caller. Unfortunately, it is relatively easy to observe migration failures when running pKVM (which uses pin_user_pages() on crosvm's virtual address space to resolve stage-2 page faults from the guest) on a 6.15-based Pixel 6 device and this results in the VM terminating prematurely. In the failure case, 'crosvm' has called mlock(MLOCK_ONFAULT) on its mapping of guest memory prior to the pinning. Subsequently, when pin_user_pages() walks the page-table, the relevant 'pte' is not present and so the faulting logic allocates a new folio, mlocks it with mlock_folio() and maps it in the page-table. Since commit 2fbb0c10d1e8 ("mm/munlock: mlock_page() munlock_page() batch by pagevec"), mlock/munlock operations on a folio (formerly page), are deferred. For example, mlock_folio() takes an additional reference on the target folio before placing it into a per-cpu 'folio_batch' for later processing by mlock_folio_batch(), which drops the refcount once the operation is complete. Processing of the batches is coupled with the LRU batch logic and can be forcefully drained with lru_add_drain_all() but as long as a folio remains unprocessed on the batch, its refcount will be elevated. This deferred batching therefore interacts poorly with the pKVM pinning scenario as we can find ourselves in a situation where the migration code fails to migrate a folio due to the elevated refcount from the pending mlock operation. Hugh Dickins adds:- !folio_test_lru() has never been a very reliable way to tell if an lru_add_drain_all() is worth calling, to remove LRU cache references to make the folio migratable: the LRU flag may be set even while the folio is held with an extra reference in a per-CPU LRU cache. 5.18 commit 2fbb0c10d1e8 may have made it more unreliable. Then 6.11 commit 33dfe9204f29 ("mm/gup: clear the LRU flag of a page before adding to LRU batch") tried to make it reliable, by moving LRU flag clearing; but missed the mlock/munlock batches, so still unreliable as reported. And it turns out to be difficult to extend 33dfe9204f29's LRU flag clearing to the mlock/munlock batches: if they do benefit from batching, mlock/munlock cannot be so effective when easily suppressed while !LRU. Instead, switch to an expected ref_count check, which was more reliable all along: some more false positives (unhelpful drains) than before, and never a guarantee that the folio will prove migratable, but better. Note on PG_private_2: ceph and nfs are still using the deprecated PG_private_2 flag, with the aid of netfs and filemap support functions. Although it is consistently matched by an increment of folio ref_count, folio_expected_ref_count() intentionally does not recognize it, and ceph folio migration currently depends on that for PG_private_2 folios to be rejected. New references to the deprecated flag are discouraged, so do not add it into the collect_longterm_unpinnable_folios() calculation: but longterm pinning of transiently PG_private_2 ceph and nfs folios (an uncommon case) may invoke a redundant lru_add_drain_all(). And this makes easy the backport to earlier releases: up to and including 6.12, btrfs also used PG_private_2, but without a ref_count increment. Note for stable backports: requires 6.16 commit 86ebd50224c0 ("mm: add folio_expected_ref_count() for reference count calculation"). Link: https://lkml.kernel.org/r/41395944-b0e3-c3ac-d648-8ddd70451d28@google.com Link: https://lkml.kernel.org/r/bd1f314a-fca1-8f19-cac0-b936c9614557@google.com Fixes: 9a4e9f3b2d73 ("mm: update get_user_pages_longterm to migrate pages allocated from CMA region") Signed-off-by: Hugh Dickins <hughd(a)google.com> Reported-by: Will Deacon <will(a)kernel.org> Closes: https://lore.kernel.org/linux-mm/20250815101858.24352-1-will@kernel.org/ Acked-by: Kiryl Shutsemau <kas(a)kernel.org> Acked-by: David Hildenbrand <david(a)redhat.com> Cc: "Aneesh Kumar K.V" <aneesh.kumar(a)kernel.org> Cc: Axel Rasmussen <axelrasmussen(a)google.com> Cc: Chris Li <chrisl(a)kernel.org> Cc: Christoph Hellwig <hch(a)infradead.org> Cc: Jason Gunthorpe <jgg(a)ziepe.ca> Cc: Johannes Weiner <hannes(a)cmpxchg.org> Cc: John Hubbard <jhubbard(a)nvidia.com> Cc: Keir Fraser <keirf(a)google.com> Cc: Konstantin Khlebnikov <koct9i(a)gmail.com> Cc: Li Zhe <lizhe.67(a)bytedance.com> Cc: Matthew Wilcox (Oracle) <willy(a)infradead.org> Cc: Peter Xu <peterx(a)redhat.com> Cc: Rik van Riel <riel(a)surriel.com> Cc: Shivank Garg <shivankg(a)amd.com> Cc: Vlastimil Babka <vbabka(a)suse.cz> Cc: Wei Xu <weixugc(a)google.com> Cc: yangge <yangge1116(a)126.com> Cc: Yuanchu Xie <yuanchu(a)google.com> Cc: Yu Zhao <yuzhao(a)google.com> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> diff --git a/mm/gup.c b/mm/gup.c index adffe663594d..82aec6443c0a 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2307,7 +2307,8 @@ static unsigned long collect_longterm_unpinnable_folios( continue; } - if (!folio_test_lru(folio) && drain_allow) { + if (drain_allow && folio_ref_count(folio) != + folio_expected_ref_count(folio) + 1) { lru_add_drain_all(); drain_allow = false; }

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FAILED: patch "[PATCH] mm/gup: check ref_count instead of lru before migration" failed to apply to 5.10-stable tree

by gregkh＠linuxfoundation.org

The patch below does not apply to the 5.10-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <stable(a)vger.kernel.org>. To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y git checkout FETCH_HEAD git cherry-pick -x 98c6d259319ecf6e8d027abd3f14b81324b8c0ad # <resolve conflicts, build, test, etc.> git commit -s git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2025092154-canon-user-98b7@gregkh' --subject-prefix 'PATCH 5.10.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ From 98c6d259319ecf6e8d027abd3f14b81324b8c0ad Mon Sep 17 00:00:00 2001 From: Hugh Dickins <hughd(a)google.com> Date: Mon, 8 Sep 2025 15:15:03 -0700 Subject: [PATCH] mm/gup: check ref_count instead of lru before migration Patch series "mm: better GUP pin lru_add_drain_all()", v2. Series of lru_add_drain_all()-related patches, arising from recent mm/gup migration report from Will Deacon. This patch (of 5): Will Deacon reports:- When taking a longterm GUP pin via pin_user_pages(), __gup_longterm_locked() tries to migrate target folios that should not be longterm pinned, for example because they reside in a CMA region or movable zone. This is done by first pinning all of the target folios anyway, collecting all of the longterm-unpinnable target folios into a list, dropping the pins that were just taken and finally handing the list off to migrate_pages() for the actual migration. It is critically important that no unexpected references are held on the folios being migrated, otherwise the migration will fail and pin_user_pages() will return -ENOMEM to its caller. Unfortunately, it is relatively easy to observe migration failures when running pKVM (which uses pin_user_pages() on crosvm's virtual address space to resolve stage-2 page faults from the guest) on a 6.15-based Pixel 6 device and this results in the VM terminating prematurely. In the failure case, 'crosvm' has called mlock(MLOCK_ONFAULT) on its mapping of guest memory prior to the pinning. Subsequently, when pin_user_pages() walks the page-table, the relevant 'pte' is not present and so the faulting logic allocates a new folio, mlocks it with mlock_folio() and maps it in the page-table. Since commit 2fbb0c10d1e8 ("mm/munlock: mlock_page() munlock_page() batch by pagevec"), mlock/munlock operations on a folio (formerly page), are deferred. For example, mlock_folio() takes an additional reference on the target folio before placing it into a per-cpu 'folio_batch' for later processing by mlock_folio_batch(), which drops the refcount once the operation is complete. Processing of the batches is coupled with the LRU batch logic and can be forcefully drained with lru_add_drain_all() but as long as a folio remains unprocessed on the batch, its refcount will be elevated. This deferred batching therefore interacts poorly with the pKVM pinning scenario as we can find ourselves in a situation where the migration code fails to migrate a folio due to the elevated refcount from the pending mlock operation. Hugh Dickins adds:- !folio_test_lru() has never been a very reliable way to tell if an lru_add_drain_all() is worth calling, to remove LRU cache references to make the folio migratable: the LRU flag may be set even while the folio is held with an extra reference in a per-CPU LRU cache. 5.18 commit 2fbb0c10d1e8 may have made it more unreliable. Then 6.11 commit 33dfe9204f29 ("mm/gup: clear the LRU flag of a page before adding to LRU batch") tried to make it reliable, by moving LRU flag clearing; but missed the mlock/munlock batches, so still unreliable as reported. And it turns out to be difficult to extend 33dfe9204f29's LRU flag clearing to the mlock/munlock batches: if they do benefit from batching, mlock/munlock cannot be so effective when easily suppressed while !LRU. Instead, switch to an expected ref_count check, which was more reliable all along: some more false positives (unhelpful drains) than before, and never a guarantee that the folio will prove migratable, but better. Note on PG_private_2: ceph and nfs are still using the deprecated PG_private_2 flag, with the aid of netfs and filemap support functions. Although it is consistently matched by an increment of folio ref_count, folio_expected_ref_count() intentionally does not recognize it, and ceph folio migration currently depends on that for PG_private_2 folios to be rejected. New references to the deprecated flag are discouraged, so do not add it into the collect_longterm_unpinnable_folios() calculation: but longterm pinning of transiently PG_private_2 ceph and nfs folios (an uncommon case) may invoke a redundant lru_add_drain_all(). And this makes easy the backport to earlier releases: up to and including 6.12, btrfs also used PG_private_2, but without a ref_count increment. Note for stable backports: requires 6.16 commit 86ebd50224c0 ("mm: add folio_expected_ref_count() for reference count calculation"). Link: https://lkml.kernel.org/r/41395944-b0e3-c3ac-d648-8ddd70451d28@google.com Link: https://lkml.kernel.org/r/bd1f314a-fca1-8f19-cac0-b936c9614557@google.com Fixes: 9a4e9f3b2d73 ("mm: update get_user_pages_longterm to migrate pages allocated from CMA region") Signed-off-by: Hugh Dickins <hughd(a)google.com> Reported-by: Will Deacon <will(a)kernel.org> Closes: https://lore.kernel.org/linux-mm/20250815101858.24352-1-will@kernel.org/ Acked-by: Kiryl Shutsemau <kas(a)kernel.org> Acked-by: David Hildenbrand <david(a)redhat.com> Cc: "Aneesh Kumar K.V" <aneesh.kumar(a)kernel.org> Cc: Axel Rasmussen <axelrasmussen(a)google.com> Cc: Chris Li <chrisl(a)kernel.org> Cc: Christoph Hellwig <hch(a)infradead.org> Cc: Jason Gunthorpe <jgg(a)ziepe.ca> Cc: Johannes Weiner <hannes(a)cmpxchg.org> Cc: John Hubbard <jhubbard(a)nvidia.com> Cc: Keir Fraser <keirf(a)google.com> Cc: Konstantin Khlebnikov <koct9i(a)gmail.com> Cc: Li Zhe <lizhe.67(a)bytedance.com> Cc: Matthew Wilcox (Oracle) <willy(a)infradead.org> Cc: Peter Xu <peterx(a)redhat.com> Cc: Rik van Riel <riel(a)surriel.com> Cc: Shivank Garg <shivankg(a)amd.com> Cc: Vlastimil Babka <vbabka(a)suse.cz> Cc: Wei Xu <weixugc(a)google.com> Cc: yangge <yangge1116(a)126.com> Cc: Yuanchu Xie <yuanchu(a)google.com> Cc: Yu Zhao <yuzhao(a)google.com> Cc: <stable(a)vger.kernel.org> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> diff --git a/mm/gup.c b/mm/gup.c index adffe663594d..82aec6443c0a 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2307,7 +2307,8 @@ static unsigned long collect_longterm_unpinnable_folios( continue; } - if (!folio_test_lru(folio) && drain_allow) { + if (drain_allow && folio_ref_count(folio) != + folio_expected_ref_count(folio) + 1) { lru_add_drain_all(); drain_allow = false; }

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