From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-230.mta1.migadu.com [95.215.58.230]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 460AB45FFA2 for ; Tue, 18 Aug 2026 13:12:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.230 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787058773; cv=none; b=T7yVrnqYwqcYW7BnzVc7leLT3wbJYymueajp2BvZxdJpHAF9VccYKUEdx+LRt9x2qEAbCVP+Iz2wYx7+G0pZIzPlAZN8Bx7NhjBHR+/2SoTRuQ/JRn7u0lYlqUCv2MCKivJOsxw3pZjnU+GzTQPgfNQpiyzoJVFm9HBbSwdU1u4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787058773; c=relaxed/simple; bh=283hSMUTf8gUQjFzslSC5pHDKwFP9cHOoLBS8rXTLtE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=n5iNj3h5+hA/ZmiwdPH+vNbbENCHJcX7RisNgysBMSqwl5OEeSLjoSsdOrg0tfAO0bErIkhVY1CjXckYzmxWpm8ZFqi5o/yGVud0YpuG3+t5xAGu7dlytt7z/FUKxVsgyGY4KtMJz81Iogz70UUUg2JvvoqAlumC4Uq5FitnlQQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=UJA8fo0N; arc=none smtp.client-ip=95.215.58.230 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="UJA8fo0N" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=283hSMUTf8gUQjFzslSC5pHDKwFP9cHOoLBS8rXTLtE=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1787058769; v=1; x=1787663569; b=UJA8fo0NMOR69hKHQibRS33CHzOeSWXnP30WedXLCzFu6kzymAsStkn6775HlO+POsYw9NL1 91km0re/pHAnCWeOwOw/OgGfyF/fA6otJuUaaZdIMs/9iUO5nR0yq3Cct8n4fnv1eO7Z3cFn6QE 0ySoVNMk9IIsDNeIyQJFjyPM= X-Envelope-To: linux-kernel@vger.kernel.org Received: from localhost (2a03:2880:10ff:28::) by mta11.migadu.com with ESMTPS id 7b774479dcad1c3c; Tue, 18 Aug 2026 13:12:49 +0000 X-Migadu-Flow: FLOW_OUT From: Usama Arif To: Andrew Morton , david@kernel.org, chrisl@kernel.org, kasong@tencent.com, ljs@kernel.org, ziy@nvidia.com, linux-mm@kvack.org Cc: ying.huang@linux.alibaba.com, Baoquan He , willy@infradead.org, youngjun.park@lge.com, hannes@cmpxchg.org, riel@surriel.com, shakeel.butt@linux.dev, alex@ghiti.fr, kas@kernel.org, baohua@kernel.org, dev.jain@arm.com, baolin.wang@linux.alibaba.com, Nico Pache , Liam R. Howlett , ryan.roberts@arm.com, Vlastimil Babka , lance.yang@linux.dev, linux-kernel@vger.kernel.org, nphamcs@gmail.com, shikemeng@huaweicloud.com, yosry@kernel.org, kernel-team@meta.com, Usama Arif Subject: [PATCH v6 09/12] mm: handle PMD swap entries in UFFDIO_MOVE Date: Tue, 18 Aug 2026 06:09:50 -0700 Message-ID: <20260818131202.494754-10-usama.arif@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260818131202.494754-1-usama.arif@linux.dev> References: <20260818131202.494754-1-usama.arif@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit move_pages_huge_pmd() returned -ENOENT for any non-trans_huge, non-migration PMD, which fails aligned UFFDIO_MOVE on a swapped-out THP -- the PMD swap entry is a perfectly valid mapping that should move whole. Splitting via the move_pages_ptes() fallback isn't a substitute either: __split_huge_pmd_locked() splits a PMD swap entry into HPAGE_PMD_NR PTE swap entries pointing at the same swap-cache folio, but move_pages_pte() refuses any swap-cache folio that is still large and returns -EBUSY. Add move_swap_pmd(), modeled on move_swap_pte(), that moves the swap entry whole-PMD and re-anchors a PMD-sized swap-cache folio's anon rmap to the destination VMA. Reject !pmd_swp_exclusive() entries with -EBUSY to preserve UFFDIO_MOVE's single-owner semantics, propagate soft-dirty, arm the UFFD marker for an RWP-registered destination, and carry the deposited page table across with the entry. The marker handling matches move_swap_pte(): the source marker rides along with the entry and is additionally armed for an RWP destination. The dispatcher in move_pages_huge_pmd() routes PMD swap entries through move_swap_pmd() after pinning the swap device and arming an mmu_notifier range. Both are guarded by CONFIG_THP_SWAP, since swap_pmd_cache_lookup() and friends only exist under CONFIG_SWAP and PMD swap entries cannot exist without CONFIG_THP_SWAP. Before moving, classify the whole PMD swap-cache range with swap_pmd_cache_lookup(). A PMD swap entry can be moved whole only if the covered range is empty or backed by one PMD-sized folio. If the range already has per-slot cache state, split the PMD swap entry and return -EAGAIN so the caller retries through the PTE path. If a PMD-sized folio is cached, lock and revalidate that it still matches the PMD swap entry. If no folio is cached, recheck all HPAGE_PMD_NR slots under both PMD locks before moving the entry; any per-slot folio that appears needs the PTE move path to update its rmap metadata. This avoids moving the PMD while cached folios still point at the old anon_vma/index. Finally, reject a PMD swap entry at the *destination* with -EEXIST in move_pages(). Such a destination is not a hole, and unlike a PMD migration entry it does not resolve on its own: pte_alloc() skips a !pmd_none PMD, pte_offset_map_rw_nolock() then fails on the non-present PMD, and move_pages() would retry the resulting -EAGAIN forever, only escapable with a fatal signal. Signed-off-by: Usama Arif --- mm/huge_memory.c | 140 ++++++++++++++++++++++++++++++++++++++++++++++- mm/userfaultfd.c | 14 +++++ 2 files changed, 153 insertions(+), 1 deletion(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 54aef8394fa25..0076d206c6a8a 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2913,6 +2913,77 @@ int change_huge_pud(struct mmu_gather *tlb, struct vm_area_struct *vma, #endif #ifdef CONFIG_USERFAULTFD +#ifdef CONFIG_THP_SWAP +/* + * Move a PMD-level swap entry from src_pmd to dst_pmd. Both PMD locks are + * acquired here; src_folio (if present) must already be locked. The deposited + * page table backing the source THP is moved across with the entry. + */ +static int move_swap_pmd(struct mm_struct *mm, struct vm_area_struct *dst_vma, + unsigned long dst_addr, unsigned long src_addr, + pmd_t *dst_pmd, pmd_t *src_pmd, + pmd_t orig_dst_pmd, pmd_t orig_src_pmd, + spinlock_t *dst_ptl, spinlock_t *src_ptl, + struct folio *src_folio, swp_entry_t entry) +{ + pgtable_t src_pgtable; + pmd_t moved_pmd; + + /* + * The folio may have been freed and reused for a different swap entry + * while it was unlocked. Re-verify the association. + */ + if (src_folio && unlikely(!folio_matches_swap_entry(src_folio, entry) || + folio_nr_pages(src_folio) != HPAGE_PMD_NR)) + return -EAGAIN; + + double_pt_lock(dst_ptl, src_ptl); + + if (!pmd_same(*src_pmd, orig_src_pmd) || + !pmd_same(*dst_pmd, orig_dst_pmd)) { + double_pt_unlock(dst_ptl, src_ptl); + return -EAGAIN; + } + + /* + * If the folio is in the swap cache, re-anchor its anon rmap to the + * destination VMA so a future swap-in fault at dst_addr finds it. + * Otherwise, re-check the whole PMD swap range: a PMD swap entry is + * only a compact encoding for 512 swap slots, and any per-slot cached + * folio would need the PTE move path to update its rmap metadata. + */ + if (src_folio) { + folio_move_anon_rmap(src_folio, dst_vma); + src_folio->index = linear_page_index(dst_vma, dst_addr); + } else { + unsigned int type = swp_type(entry); + pgoff_t offset = swp_offset(entry); + int i; + + for (i = 0; i < HPAGE_PMD_NR; i++) { + if (swap_cache_has_folio(swp_entry(type, offset + i))) { + double_pt_unlock(dst_ptl, src_ptl); + return -EAGAIN; + } + } + } + + moved_pmd = pmdp_huge_get_and_clear(mm, src_addr, src_pmd); + if (pgtable_supports_soft_dirty()) + moved_pmd = pmd_swp_mksoft_dirty(moved_pmd); + /* Re-arm RWP on the moved swap entry if dst_vma is RWP-registered. */ + if (userfaultfd_rwp(dst_vma)) + moved_pmd = pmd_swp_mkuffd(moved_pmd); + set_pmd_at(mm, dst_addr, dst_pmd, moved_pmd); + + src_pgtable = pgtable_trans_huge_withdraw(mm, src_pmd); + pgtable_trans_huge_deposit(mm, dst_pmd, src_pgtable); + + double_pt_unlock(dst_ptl, src_ptl); + return 0; +} +#endif /* CONFIG_THP_SWAP */ + /* * The PT lock for src_pmd and dst_vma/src_vma (for reading) are locked by * the caller, but it must return after releasing the page_table_lock. @@ -2947,11 +3018,78 @@ int move_pages_huge_pmd(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, pm } if (!pmd_trans_huge(src_pmdval)) { - spin_unlock(src_ptl); if (pmd_is_migration_entry(src_pmdval)) { + spin_unlock(src_ptl); pmd_migration_entry_wait(mm, src_pmd); return -EAGAIN; } +#ifdef CONFIG_THP_SWAP + if (pmd_is_swap_entry(src_pmdval)) { + swp_entry_t entry; + struct swap_info_struct *si; + enum swap_pmd_cache cache_state; + + /* + * UFFDIO_MOVE on anon mappings requires single-owner + * semantics; refuse to move a shared swap entry. + */ + if (!pmd_swp_exclusive(src_pmdval)) { + spin_unlock(src_ptl); + return -EBUSY; + } + + entry = softleaf_from_pmd(src_pmdval); + spin_unlock(src_ptl); + + /* Pin the swap device against a racing swapoff. */ + si = get_swap_device(entry); + if (unlikely(!si)) + return -EAGAIN; + + src_folio = NULL; + cache_state = swap_pmd_cache_lookup(entry, &src_folio); + if (cache_state == SWAP_PMD_CACHE_SPLIT) { + put_swap_device(si); + __split_huge_pmd(src_vma, src_pmd, src_addr, false); + return -EAGAIN; + } + + mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, + mm, src_addr, + src_addr + HPAGE_PMD_SIZE); + mmu_notifier_invalidate_range_start(&range); + + if (src_folio) { + folio_lock(src_folio); + if (!folio_matches_swap_entry(src_folio, entry) || + folio_nr_pages(src_folio) != HPAGE_PMD_NR) { + err = -EAGAIN; + folio_unlock(src_folio); + folio_put(src_folio); + mmu_notifier_invalidate_range_end(&range); + put_swap_device(si); + __split_huge_pmd(src_vma, src_pmd, + src_addr, false); + return err; + } + } + + dst_ptl = pmd_lockptr(mm, dst_pmd); + err = move_swap_pmd(mm, dst_vma, dst_addr, src_addr, + dst_pmd, src_pmd, dst_pmdval, + src_pmdval, dst_ptl, src_ptl, + src_folio, entry); + + mmu_notifier_invalidate_range_end(&range); + if (src_folio) { + folio_unlock(src_folio); + folio_put(src_folio); + } + put_swap_device(si); + return err; + } +#endif /* CONFIG_THP_SWAP */ + spin_unlock(src_ptl); return -ENOENT; } diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 23fb68fce000e..3692ffb326ffd 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -2106,6 +2106,20 @@ static ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start, break; } + /* + * A PMD swap entry at dst is a swapped-out THP, not a hole, + * and unlike a PMD migration entry it will not resolve on its + * own. Nothing below faults it back in: pte_alloc() skips a + * !pmd_none PMD, pte_offset_map_rw_nolock() then fails on the + * non-present PMD, and the -EAGAIN that produces would be + * retried forever by the loop below. Be strict, exactly as for + * a present THP. + */ + if (unlikely(pmd_is_swap_entry(dst_pmdval))) { + err = -EEXIST; + break; + } + ptl = pmd_trans_huge_lock(src_pmd, src_vma); if (ptl) { /* Check if we can move the pmd without splitting it. */ -- 2.53.0-Meta