From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 17037606A327 for ; Sat, 31 Oct 2026 09:44:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=lists.infradead.org header.i=@lists.infradead.org header.a=rsa-sha256 header.s=bombadil.20210309 header.b=MAxzQ8zk; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=iBtzxhIJ DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Cc:To:In-Reply-To:References :Message-Id:Content-Transfer-Encoding:Content-Type:MIME-Version:Subject:Date: From:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Unsubscribe-Post: List-Owner; bh=QNhskX8AAxaa5M1fwAoCqUvge2t9q0zs/kkghFS30Mk=; b=MAxzQ8zkrZsMO3 qeCCaDJJAmDAlfZkMdTWC4FwKaXINZ1Y6AoNk5lAIJ1ZZObLHI1vl0ROt+tZ1mRrKaN4Zq9a6BXm4 Y+Z4ipjOadqBQ7GLGRWA+PmI34g+oEn7sZMYLwHy1NBnskPMXtO5NeSBZXI/ocJXjHgVAVQysN0Hd /xcbDHJFsYU9GBNqszgtw56Q4ovSvdTn2MbMmfe4S6tIDrYRzo+YQiSlvVv3wEHlCmSPTs0nLTART UVBkQ0hNgQH7SNrTGUkmlJCNfR6W8agLdv2RncOkSSfPd4KAVxFYrnXWAteqUpIazMay1FlfWyvuy 460ovMoQnPtfFPvPdVQg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.100.1 #2 (Red Hat Linux)) id 1xN5dw-0000000DA2Q-3QOx; Sat, 31 Oct 2026 09:44:56 +0000 Received: from tor.source.kernel.org ([2600:3c04:e001:324:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.100.1 #2 (Red Hat Linux)) id 1xN5dw-0000000DA28-1M3B for kexec@lists.infradead.org; Sat, 31 Oct 2026 09:44:56 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id BD4AA600E4; Sat, 31 Oct 2026 09:44:55 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A2F1B1F000C1; Sat, 31 Oct 2026 09:44:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793439895; bh=QNhskX8AAxaa5M1fwAoCqUvge2t9q0zs/kkghFS30Mk=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=iBtzxhIJ0CsWoL5jGThlLVtJSXfi+Jad6c/A4voYQdFAsTMOdaZi4mA4eSe0oCg2q S+//+VEHuK0a+kG7Uh0zRCV3w4MEipyuoa1zhnUYhGG3J9a3T2BwE1eP6wdYcPsfcI +8nTxbf0i5uqlPb+igx6Hb8Os47pk6uQmxP8WYxw1FYXXSuZQcYRuFQqh0DiBKeuV0 Syt0t0ndqaTLZLGsh1BSjcWBuWAqfVm2RfttK6PZxS4mBh1dbHUuyUv2/tLVOt06tI 8Wb/MvM2ZMg32waas3hRogrSp0AZqDaPqj/9VHe7hnktu1KBMAk47Y3zfi2LwijIcM 68+XyLRvIfitw== From: "David Hildenbrand (Arm)" Date: Sat, 31 Oct 2026 10:39:47 +0100 Subject: [PATCH v3 18/47] mm/khugepaged: check if PTE table is empty in try_collapse_pte_mapped_thp() X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261031-fixes_core-v3-18-d6437171ecc3@kernel.org> References: <20261031-fixes_core-v3-0-d6437171ecc3@kernel.org> In-Reply-To: <20261031-fixes_core-v3-0-d6437171ecc3@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, Muhammad Usama Anjum , "David Hildenbrand (Arm)" X-Mailer: b4 0.16.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=5693; i=david@kernel.org; h=from:subject:message-id; bh=N8E06eBkw92846cTEzxygYjVlauKxWEwZ4cBWEIgU4g=; b=owGbwMvMwCF2/OVpCdfQ3ZWMp9WSGLKebk/vWGhsU3Fl1vx/nV+sF5XNe8h1fsNMQU2HieGGB XyzutwdO0pZGMQ4GGTFFFmCgu8bvHy5rrbajY8ZZg4rE8gQBi5OAZjInTpGht3vN894nPY5eGah juQtF96fwtcuWRy5FXSm8uj5zGXXzR8x/HdvW+Rf+nuv1Nm7l0L3/6nufJtccORf6gcPkbTo0M+ TtvMCAA== X-Developer-Key: i=david@kernel.org; a=openpgp; fpr=1BD9CAAD735C4C3A460DFCCA4DDE10F700FF835A X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "kexec" X-Spam-Status: No, score=-18.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 The existing code is rather horrible and already resulted in bugs in the past: we special-case UFFD inserting anonymous folios by grabbing the PMD lock early, but ignore any other markers (guard, poison through uffd) that could have been inserted into the page table in the meantime, effectively dropping them. Let's just unify and simplify the locking: try to grab the PMD table lock and if that fails, flush the TLB, drop the PTE lock, take PT locks in the right order and check if the page table is still empty. We still perform the heavy lifting (zapping the folio ptes) under PTE table lock only. Include for now, as x86's flush_tlb_range() macro depends on hugetlb helpers. This dependency needs a separate cleanup. Both issues this fixes are rather corner cases. Let's not CC stable for now. Fixes: f807123d578d ("mm: allow guard regions in file-backed and read-only mappings") Fixes: 1043173eb5eb ("mm/khugepaged: collapse_pte_mapped_thp() with mmap_read_lock()") Tested-by: Gregory Price (Meta) Reviewed-by: Gregory Price (Meta) Tested-by: Muhammad Usama Anjum Signed-off-by: David Hildenbrand (Arm) --- mm/khugepaged.c | 64 ++++++++++++++++++++++++++++----------------------------- 1 file changed, 31 insertions(+), 33 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index ce794d9760a87..ad07c8caa3bd9 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -10,6 +10,7 @@ #include #include #include +#include #include #include #include @@ -1832,6 +1833,17 @@ static enum scan_result set_huge_pmd(struct vm_area_struct *vma, unsigned long a return SCAN_SUCCEED; } +static bool pte_table_empty(pte_t *pte) +{ + int i; + + for (i = 0; i < HPAGE_PMD_NR; i++, pte++) { + if (!pte_none(ptep_get(pte))) + return false; + } + return true; +} + static enum scan_result try_collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr, bool install_pmd) { @@ -1935,33 +1947,14 @@ static enum scan_result try_collapse_pte_mapped_thp(struct mm_struct *mm, unsign } pte_unmap_unlock(start_pte, ptl); - ptl = NULL; mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, haddr, haddr + HPAGE_PMD_SIZE); mmu_notifier_invalidate_range_start(&range); notified = true; - /* - * pmd_lock covers a wider range than ptl, and (if split from mm's - * page_table_lock) ptl nests inside pml. The less time we hold pml, - * the better; but userfaultfd's mfill_atomic_pte() on a private VMA - * inserts a valid as-if-COWed PTE without even looking up page cache. - * So page lock of folio does not protect from it, so we must not drop - * ptl before pgt_pmd is removed, so uffd private needs pml taken now. - */ - if (userfaultfd_armed(vma) && !(vma->vm_flags & VM_SHARED)) - pml = pmd_lock(mm, pmd); - - start_pte = pte_offset_map_rw_nolock(mm, pmd, haddr, &pgt_pmd, &ptl); + start_pte = pte_offset_map_lock(mm, pmd, haddr, &ptl); if (!start_pte) goto abort; - if (!pml) - spin_lock(ptl); - else if (ptl != pml) - spin_lock_nested(ptl, SINGLE_DEPTH_NESTING); - - if (unlikely(!pmd_same(pgt_pmd, pmdp_get_lockless(pmd)))) - goto abort; /* step 2: clear page table and adjust rmap */ for (i = 0, addr = haddr, pte = start_pte; i < HPAGE_PMD_NR; @@ -1992,10 +1985,7 @@ static enum scan_result try_collapse_pte_mapped_thp(struct mm_struct *mm, unsign nr_batch_ptes = folio_pte_batch(folio, pte, ptent, max_nr_batch_ptes); - /* - * Must clear entry, or a racing truncate may re-remove it. - * TLB flush can be left until pmdp_collapse_flush() does it. - */ + /* Must clear entry, or a racing truncate may re-remove it. */ ptent = get_and_clear_ptes(mm, addr, pte, nr_batch_ptes); if (pte_dirty(ptent)) folio_mark_dirty(folio); @@ -2003,25 +1993,33 @@ static enum scan_result try_collapse_pte_mapped_thp(struct mm_struct *mm, unsign nr_mapped_ptes += nr_batch_ptes; } - if (!pml) - spin_unlock(ptl); - /* step 3: set proper refcount and mm_counters. */ if (nr_mapped_ptes) { folio_ref_sub(folio, nr_mapped_ptes); add_mm_counter(mm, mm_counter_file(folio), -nr_mapped_ptes); } - /* step 4: remove empty page table */ - if (!pml) { + /* step 4: acquire the PMD lock and remove the empty page table */ + pml = pmd_lockptr(mm, pmd); + if (ptl != pml && !spin_trylock(pml)) { + /* We must flush before dropping the PTL. */ + if (nr_mapped_ptes) + flush_tlb_range(vma, haddr, end); + pte_unmap_unlock(start_pte, ptl); + ptl = NULL; + pml = pmd_lock(mm, pmd); + start_pte = pte_offset_map_rw_nolock(mm, pmd, haddr, &pgt_pmd, &ptl); + if (!start_pte) + goto unlock; if (ptl != pml) spin_lock_nested(ptl, SINGLE_DEPTH_NESTING); - if (unlikely(!pmd_same(pgt_pmd, pmdp_get_lockless(pmd)))) { - flush_tlb_mm(mm); + + if (!pte_table_empty(start_pte)) goto unlock; - } } + + /* This also flushes the zapped folio ptes properly. */ pgt_pmd = pmdp_collapse_flush(vma, haddr, pmd); pmdp_get_lockless_sync(); pte_unmap_unlock(start_pte, ptl); @@ -2042,7 +2040,7 @@ static enum scan_result try_collapse_pte_mapped_thp(struct mm_struct *mm, unsign goto drop_folio; abort: if (nr_mapped_ptes) { - flush_tlb_mm(mm); + flush_tlb_range(vma, haddr, end); folio_ref_sub(folio, nr_mapped_ptes); add_mm_counter(mm, mm_counter_file(folio), -nr_mapped_ptes); } -- 2.43.0