From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 30CABFEE4ED for ; Sat, 28 Feb 2026 14:06:24 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 3FF676B0005; Sat, 28 Feb 2026 09:06:23 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 3AD706B0088; Sat, 28 Feb 2026 09:06:23 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2A26A6B0089; Sat, 28 Feb 2026 09:06:23 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 198C06B0005 for ; Sat, 28 Feb 2026 09:06:23 -0500 (EST) Received: from smtpin19.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 8FC5B897C2 for ; Sat, 28 Feb 2026 14:06:22 +0000 (UTC) X-FDA: 84494040204.19.A03AB2A Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf21.hostedemail.com (Postfix) with ESMTP id C4D581C0004 for ; Sat, 28 Feb 2026 14:06:20 +0000 (UTC) Authentication-Results: imf21.hostedemail.com; dkim=none; spf=pass (imf21.hostedemail.com: domain of dev.jain@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=dev.jain@arm.com; dmarc=pass (policy=none) header.from=arm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1772287581; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:references; bh=t0+Pm93/3ss9gX6u1pYsXzkNT77jHWIcm5JBaNmPAZA=; b=jhpahttrmz0yqVLjhl+0xHcwxMyfVLsUV87lWGPEiQ+LOz3zAY1YRwRD9w/XMlEJRMMF95 JPLc76xGo8eh+S7vGzsOPx8Wa43/RVBDuThJK2y3tr/30JAxT8LZBuK2xPvK5H9ik2PovQ qT9ow4cqN38aXZBT/yYd6cHk+rbEXLs= ARC-Authentication-Results: i=1; imf21.hostedemail.com; dkim=none; spf=pass (imf21.hostedemail.com: domain of dev.jain@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=dev.jain@arm.com; dmarc=pass (policy=none) header.from=arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1772287581; a=rsa-sha256; cv=none; b=C3ddBct74SPmngZ2FsdCvepdQwF75bChWR/jj7bHB+BDIBENx94lpkJ7GwwrkIrzSOjVoC WHNh8RYsr5uTP4z9FpS9jExEk/5MiIgvqLQg0d9kpFc4k4aXzgNZ0SzCQtRPy8G93XUsfj kUy38tL8WTug9A/G9QZccy6gHl3hGRo= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 465731516; Sat, 28 Feb 2026 06:06:13 -0800 (PST) Received: from a080796.blr.arm.com (a080796.arm.com [10.164.21.51]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 30F4B3F7BD; Sat, 28 Feb 2026 06:06:14 -0800 (PST) From: Dev Jain To: akpm@linux-foundation.org, david@kernel.org, lorenzo.stoakes@oracle.com Cc: riel@surriel.com, Liam.Howlett@oracle.com, vbabka@kernel.org, harry.yoo@oracle.com, jannh@google.com, baohua@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ryan.roberts@arm.com, anshuman.khandual@arm.com, Dev Jain , stable Subject: [PATCH v2] mm/rmap: fix incorrect pte restoration for lazyfree folios Date: Sat, 28 Feb 2026 19:35:40 +0530 Message-Id: <20260228140540.1774748-1-dev.jain@arm.com> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: C4D581C0004 X-Rspamd-Server: rspam08 X-Stat-Signature: se683rj4adcyp6cttkfqm77ahfd76nkg X-HE-Tag: 1772287580-672667 X-HE-Meta: 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: We batch unmap anonymous lazyfree folios by folio_unmap_pte_batch. If the batch has a mix of writable and non-writable bits, we may end up setting the entire batch writable. Fix this by respecting writable bit during batching. Although on a successful unmap of a lazyfree folio, the soft-dirty bit is lost, preserve it on pte restoration by respecting the bit during batching, to make the fix consistent w.r.t both writable bit and soft-dirty bit. I was able to write the below reproducer and crash the kernel. Explanation of reproducer (set 64K mTHP to always): Fault in a 64K large folio. Split the VMA at mid-point with MADV_DONTFORK. fork() - parent points to the folio with 8 writable ptes and 8 non-writable ptes. Merge the VMAs with MADV_DOFORK so that folio_unmap_pte_batch() can determine all the 16 ptes as a batch. Do MADV_FREE on the range to mark the folio as lazyfree. Write to the memory to dirty the pte, eventually rmap will dirty the folio. Then trigger reclaim, we will hit the pte restoration path, and the kernel will crash with the following trace: [ 21.134473] kernel BUG at mm/page_table_check.c:118! [ 21.134497] Internal error: Oops - BUG: 00000000f2000800 [#1] SMP [ 21.135917] Modules linked in: [ 21.136085] CPU: 1 UID: 0 PID: 1735 Comm: dup-lazyfree Not tainted 7.0.0-rc1-00116-g018018a17770 #1028 PREEMPT [ 21.136858] Hardware name: linux,dummy-virt (DT) [ 21.137019] pstate: 21400005 (nzCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--) [ 21.137308] pc : page_table_check_set+0x28c/0x2a8 [ 21.137607] lr : page_table_check_set+0x134/0x2a8 [ 21.137885] sp : ffff80008a3b3340 [ 21.138124] x29: ffff80008a3b3340 x28: fffffdffc3d14400 x27: ffffd1a55e03d000 [ 21.138623] x26: 0040000000000040 x25: ffffd1a55f7dd000 x24: 0000000000000001 [ 21.139045] x23: 0000000000000001 x22: 0000000000000001 x21: ffffd1a55f217f30 [ 21.139629] x20: 0000000000134521 x19: 0000000000134519 x18: 005c43e000040000 [ 21.140027] x17: 0001400000000000 x16: 0001700000000000 x15: 000000000000ffff [ 21.140578] x14: 000000000000000c x13: 005c006000000000 x12: 0000000000000020 [ 21.140828] x11: 0000000000000000 x10: 005c000000000000 x9 : ffffd1a55c079ee0 [ 21.141077] x8 : 0000000000000001 x7 : 005c03e000040000 x6 : 000000004000ffff [ 21.141490] x5 : ffff00017fffce00 x4 : 0000000000000001 x3 : 0000000000000002 [ 21.141741] x2 : 0000000000134510 x1 : 0000000000000000 x0 : ffff0000c08228c0 [ 21.141991] Call trace: [ 21.142093] page_table_check_set+0x28c/0x2a8 (P) [ 21.142265] __page_table_check_ptes_set+0x144/0x1e8 [ 21.142441] __set_ptes_anysz.constprop.0+0x160/0x1a8 [ 21.142766] contpte_set_ptes+0xe8/0x140 [ 21.142907] try_to_unmap_one+0x10c4/0x10d0 [ 21.143177] rmap_walk_anon+0x100/0x250 [ 21.143315] try_to_unmap+0xa0/0xc8 [ 21.143441] shrink_folio_list+0x59c/0x18a8 [ 21.143759] shrink_lruvec+0x664/0xbf0 [ 21.144043] shrink_node+0x218/0x878 [ 21.144285] __node_reclaim.constprop.0+0x98/0x338 [ 21.144763] user_proactive_reclaim+0x2a4/0x340 [ 21.145056] reclaim_store+0x3c/0x60 [ 21.145216] dev_attr_store+0x20/0x40 [ 21.145585] sysfs_kf_write+0x84/0xa8 [ 21.145835] kernfs_fop_write_iter+0x130/0x1c8 [ 21.145994] vfs_write+0x2b8/0x368 [ 21.146119] ksys_write+0x70/0x110 [ 21.146240] __arm64_sys_write+0x24/0x38 [ 21.146380] invoke_syscall+0x50/0x120 [ 21.146513] el0_svc_common.constprop.0+0x48/0xf8 [ 21.146679] do_el0_svc+0x28/0x40 [ 21.146798] el0_svc+0x34/0x110 [ 21.146926] el0t_64_sync_handler+0xa0/0xe8 [ 21.147074] el0t_64_sync+0x198/0x1a0 [ 21.147225] Code: f9400441 b4fff241 17ffff94 d4210000 (d4210000) [ 21.147440] ---[ end trace 0000000000000000 ]--- #define _GNU_SOURCE #include #include #include #include #include #include #include #include void write_to_reclaim() { const char *path = "/sys/devices/system/node/node0/reclaim"; const char *value = "409600000000"; int fd = open(path, O_WRONLY); if (fd == -1) { perror("open"); exit(EXIT_FAILURE); } if (write(fd, value, sizeof("409600000000") - 1) == -1) { perror("write"); close(fd); exit(EXIT_FAILURE); } printf("Successfully wrote %s to %s\n", value, path); close(fd); } int main() { char *ptr = mmap((void *)(1UL << 30), 1UL << 16, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); if ((unsigned long)ptr != (1UL << 30)) { perror("mmap"); return 1; } /* a 64K folio gets faulted in */ memset(ptr, 0, 1UL << 16); /* 32K half will not be shared into child */ if (madvise(ptr, 1UL << 15, MADV_DONTFORK)) { perror("madvise madv dontfork"); return 1; } pid_t pid = fork(); if (pid < 0) { perror("fork"); return 1; } else if (pid == 0) { sleep(15); } else { /* merge VMAs. now first half of the 16 ptes are writable, the other half not. */ if (madvise(ptr, 1UL << 15, MADV_DOFORK)) { perror("madvise madv fork"); return 1; } if (madvise(ptr, (1UL << 16), MADV_FREE)) { perror("madvise madv free"); return 1; } /* dirty the large folio */ (*ptr) += 10; write_to_reclaim(); // sleep(10); waitpid(pid, NULL, 0); } } Fixes: 354dffd29575 ("mm: support batched unmap for lazyfree large folios during reclamation") Cc: stable Signed-off-by: Dev Jain --- v1->v2: - Just respect the writable bit instead of hacking in a pte_wrprotect() in failure path - Also handle soft-dirty bit Based on mm-unstable (df9c51269a5e). mm/rmap.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/mm/rmap.c b/mm/rmap.c index bff8f222004e4..fb64829913052 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1955,7 +1955,17 @@ static inline unsigned int folio_unmap_pte_batch(struct folio *folio, if (userfaultfd_wp(vma)) return 1; - return folio_pte_batch(folio, pvmw->pte, pte, max_nr); + if (!folio_test_anon(folio)) + return folio_pte_batch(folio, pvmw->pte, pte, max_nr); + + /* + * For anon folios, if unmap fails, we need to restore the ptes. + * To avoid accidentally upgrading write permissions for ptes that + * were not originally writable, and to avoid losing the soft-dirty + * bit, use the appropriate FPB flags. + */ + return folio_pte_batch_flags(folio, vma, pvmw->pte, &pte, max_nr, + FPB_RESPECT_WRITE | FPB_RESPECT_SOFT_DIRTY); } /* -- 2.34.1