From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793057434; b=F6TdEslQreUDmGc9gRtt8MqiOrOo6JLnkvlOLYks8MtgnysO4/pUWn4JwPwi7V6vm0ka XQwk3hiPyfDBVjGZcFAF8+EeCtfh900UMvBjLkAOQvaKHTN3BnZ8FKVSO75UxYoGlprxT +Tv337AkSPxMAH9GaSKm595cDp1is9Rc0kp8YIYpYtVIsr8H2/mWe7N5+CYC89QDGcLWJ a9h5aRq+7imkxiXQDRINUnTGZvHKQEbgTBfqsLGATlDuseW6dRX6V4WR9L9GY2fXaSoXu vcIlbhcA4ksMyGgvXSeuN1zSYnuGAK7Q7hcWD2VicRM93dIYqOPgLodmFLQQwuf3l8w== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793057434; h=Received:DKIM-Signature:From:Date:Subject:MIME-Version:Content-Type: Content-Transfer-Encoding:Message-Id:References:In-Reply-To:To:Cc: X-Mailer:X-Developer-Signature:X-Developer-Key; bh=QD80RIB+y4ufuur+YyQBCtVBuNIRW9PI0dOqkUCl6r4=; b=pdwp8oyIzNkeTBVDhrzIFjeGoUdaH9PIs0bkc116Z/QroWxkXAY6oUkxgQRHFtxLtyWD x47cndy75YZiiqc0RmQCBpCnKXUo5h2XUYk9LB6yoCVediyNDdRmyfNnRBCRsT62cgxPA bgvIv9iHwXzWcDTOaEDbPZMEtuOdk+8nCOeq1YXTymicCItbmzBMztNaTaXLtiDV+qxhE UgEDKI/VF8h+SJa0z+A/np8OgI8DizrHzocLFjBMM4Qj3bFCL8kvB2NjZHbQ3Dtl6SLCT paTHquKz9XMp69HgwqpFR/uNOFgrqUlQfQ94ilGaf8fpYNGglGxnR+1lcRR0VBSKqGQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=Idfp5FdH; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8B059606A31A; Mon, 26 Oct 2026 23:30:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=Idfp5FdH Received: by smtp.kernel.org (Postfix) with ESMTPSA id 699E61F031E4; Mon, 26 Oct 2026 23:30:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793057434; bh=QD80RIB+y4ufuur+YyQBCtVBuNIRW9PI0dOqkUCl6r4=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=Idfp5FdHu05jmgG2gxrdPm9pJx1n3xB1zoPEfEOUq9+fiGYk98OuHmK/JnwLyctpJ 5/yyl6bqnxBDnMBMUJZuD+2fPDwfAmFHhQ4wS6AYY9RVV8oYlRAzYfMbteM5kb4BvA tcLdxABufX1OTiZA/39+6NKUjEbIDyPAjBkWNRfNoNk/GFP8kQDXlHHt3Vy5+deFdu 9An1+YVChNv4Y8ZrFy7+/OQeyjP8Hn4HTV/BtEwa20A559hfO3FvjhnpGrlzvbgJAy aiAMr0KsMDnT2wNRSCDWYgsCnM5+Kg5iaAPY3I23sM+oY4B8yPtRWlDPSi8Z/DrGd2 jOboFyyDzd0SA== From: "David Hildenbrand (Arm)" Date: Tue, 27 Oct 2026 00:18:00 +0100 Subject: [PATCH 40/46] mm/ksm: check large swap-cache folios before mapping them X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261027-fixes_core-v1-40-6f74bec9a5bb@kernel.org> References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> In-Reply-To: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> To: Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Pedro Falcato , Hugh Dickins , Pasha Tatashin , Pratyush Yadav , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Kiryl Shutsemau , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, Chris Mason , stable@vger.kernel.org, "David Hildenbrand (Arm)" X-Mailer: b4 0.16.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=5706; i=david@kernel.org; h=from:subject:message-id; bh=NNztKZDxEKa7XxQhow2LeYex7WrWA250Qi1z9GReFZc=; b=owGbwMvMwCF2/OVpCdfQ3ZWMp9WSGLLu35/h0hqzoXUNzwMtNbOlZv7sCk5VsXdDvmzqXSypY 1ovP7G/o5SFQYyDQVZMkSUo+L7By5fraqvd+Jhh5rAygQxh4OIUgIm8zWJk+CR7I3FP9F7DR0sz m5emXImYV6B0b7O1X4VgdPHFFW++lzAyHFR8+yHg7uTiCdsPst/rZti0qS5cdbtf0FLH5xq1vy9 MYQMA X-Developer-Key: i=david@kernel.org; a=openpgp; fpr=1BD9CAAD735C4C3A460DFCCA4DDE10F700FF835A From: Chris Mason KSM folios are always small, but their shared swap slots can be read back as part of a large folio in the swap cache. ksm_might_need_to_copy() skips large folios, so another process can map a page with an incompatible anon_vma or page index. Reverse mapping then cannot find the new mapping, preventing migration or reclaim. Apply the same compatibility checks to large folios as to small ones. Pass the page corresponding to the swap entry and copy only that page when necessary. In do_swap_page()'s copy path, decrement only that slot's swap count, because the source swap-cache folio can now be large. Fix generated by an LLM and sent by Chris Mason in private. Fixes: f1879e8a0c60 ("mm, swap: never bypass the swap cache even for SWP_SYNCHRONOUS_IO") Cc: stable@vger.kernel.org Signed-off-by: Chris Mason Signed-off-by: David Hildenbrand (Arm) --- include/linux/ksm.h | 6 +++--- mm/ksm.c | 22 ++++++++++++---------- mm/memory.c | 5 +++-- mm/swapfile.c | 3 ++- 4 files changed, 20 insertions(+), 16 deletions(-) diff --git a/include/linux/ksm.h b/include/linux/ksm.h index d39d0d5483a23..a0d358a1feb63 100644 --- a/include/linux/ksm.h +++ b/include/linux/ksm.h @@ -91,8 +91,8 @@ static inline void ksm_exit(struct mm_struct *mm) * We'd like to make this conditional on vma->vm_flags & VM_MERGEABLE, * but what if the vma was unmerged while the page was swapped out? */ -struct folio *ksm_might_need_to_copy(struct folio *folio, - struct vm_area_struct *vma, unsigned long addr); +struct folio *ksm_might_need_to_copy(struct folio *folio, struct page *page, + struct vm_area_struct *vma, unsigned long addr); void rmap_walk_ksm(struct folio *folio, struct rmap_walk_control *rwc); void folio_migrate_ksm(struct folio *newfolio, struct folio *folio); @@ -145,7 +145,7 @@ static inline int ksm_madvise(struct vm_area_struct *vma, unsigned long start, } static inline struct folio *ksm_might_need_to_copy(struct folio *folio, - struct vm_area_struct *vma, unsigned long addr) + struct page *page, struct vm_area_struct *vma, unsigned long addr) { return folio; } diff --git a/mm/ksm.c b/mm/ksm.c index e050b1bdf810d..e95f6b6723602 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -3138,19 +3138,20 @@ void __ksm_exit(struct mm_struct *mm) } static bool folio_anon_rmap_compatible(const struct folio *folio, - struct vm_area_struct *vma, unsigned long addr) + const struct page *page, struct vm_area_struct *vma, + unsigned long addr) { const struct anon_vma *anon_vma = folio_anon_vma(folio); struct anon_vma_chain *avc; VM_WARN_ON_ONCE_FOLIO(!folio_test_locked(folio), folio); - VM_WARN_ON_ONCE_FOLIO(folio_test_large(folio), folio); + VM_WARN_ON_ONCE_FOLIO(page_folio(page) != folio, folio); VM_WARN_ON_ONCE_FOLIO(folio_test_ksm(folio), folio); vma_assert_stabilised(vma); if (!anon_vma) return true; - if (folio->index != linear_anon_page_index(vma, addr)) + if (page_pgoff(folio, page) != linear_anon_page_index(vma, addr)) return false; /* @@ -3167,20 +3168,21 @@ static bool folio_anon_rmap_compatible(const struct folio *folio, return false; } -struct folio *ksm_might_need_to_copy(struct folio *folio, - struct vm_area_struct *vma, unsigned long addr) +struct folio *ksm_might_need_to_copy(struct folio *folio, struct page *page, + struct vm_area_struct *vma, unsigned long addr) { - struct page *page = folio_page(folio, 0); struct folio *new_folio; - if (folio_test_large(folio)) - return folio; - + /* + * A KSM folio is small, but the slot that it left behind can be swapped + * in as a part of a large folio by one of the processes that shared it. + * So test, and copy, the page of the slot. + */ if (folio_test_ksm(folio)) { if (folio_stable_node(folio) && !(ksm_run & KSM_RUN_UNMERGE)) return folio; /* no need to copy it */ - } else if (folio_anon_rmap_compatible(folio, vma, addr)) { + } else if (folio_anon_rmap_compatible(folio, page, vma, addr)) { return folio; /* still no need to copy it */ } if (PageHWPoison(page)) diff --git a/mm/memory.c b/mm/memory.c index 230a2f4dafa13..be4c05db37d33 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -5096,7 +5096,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) * folio->index of non-ksm folios would be nonlinear inside the * anon VMA -- the ksm flag is lost on actual swapout. */ - folio = ksm_might_need_to_copy(folio, vma, vmf->address); + folio = ksm_might_need_to_copy(folio, page, vma, vmf->address); if (unlikely(!folio)) { ret = VM_FAULT_OOM; folio = swapcache; @@ -5278,7 +5278,8 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) if (unlikely(folio != swapcache)) { folio_add_new_anon_rmap(folio, vma, address, RMAP_EXCLUSIVE); folio_add_lru_vma(folio, vma); - folio_put_swap(swapcache, NULL); + folio_put_swap(swapcache, + folio_file_page(swapcache, swp_offset(entry))); } else if (!folio_test_anon(folio)) { /* * We currently only expect !anon folios that are fully diff --git a/mm/swapfile.c b/mm/swapfile.c index 254ce86fa923e..71ef9e2efb3a9 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -2514,7 +2514,8 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd, return 0; swapcache = folio; - folio = ksm_might_need_to_copy(folio, vma, addr); + folio = ksm_might_need_to_copy(folio, + folio_file_page(folio, swp_offset(entry)), vma, addr); if (unlikely(!folio)) return -ENOMEM; else if (unlikely(folio == ERR_PTR(-EHWPOISON))) { -- 2.43.0