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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 1BA13CAC5B8 for ; Mon, 6 Oct 2025 13:17:58 +0000 (UTC) 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:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=OnMHepD+4WUs5JH2g5ZG/hZQqmEj6Pg6RLIUw2l4UoU=; b=tRssMiEOOVFMkU/kJKi902LwM/ KtUzawtGUV+Z5AO1TuDQm6UhEBkN1hDRssS+csdM+z8+FQ9gGgB8CgBjRgVhzql1+0TE4+5t71mtb idyHZl2zyXhzDLhxQw0dG6MOC0t5Z8yxfsDA5XEo8H9VZCQZX8TkfYDj9VnRyUar8yfjZ4OCbsnMj enHK8maUi1Y60Onel96zL2oVZHomzJMZZfv9c/OaD6C9qZP4Fh/Y59dWw/kzbKdGR6CHMc/fJo1J1 IbhH5CLQpdsohAlVB9cbGZLI6qtycotqlCMq3TuS+b5QuBD6gJjfnCP0On4hPRR4/hKtDwrbSGmSh HGQCFpow==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1v5l67-000000004x6-3PKq; Mon, 06 Oct 2025 13:17:51 +0000 Received: from sea.source.kernel.org ([172.234.252.31]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1v5l64-000000004wM-2kJL for linux-arm-kernel@lists.infradead.org; Mon, 06 Oct 2025 13:17:49 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 80D234341F; Mon, 6 Oct 2025 13:17:45 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E3348C4CEF5; Mon, 6 Oct 2025 13:17:43 +0000 (UTC) Date: Mon, 6 Oct 2025 14:17:40 +0100 From: Catalin Marinas To: David Hildenbrand Cc: syzbot , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, will@kernel.org, Kefeng Wang Subject: Re: [syzbot] [arm?] WARNING in copy_highpage Message-ID: References: <68dda1ae.a00a0220.102ee.0065.GAE@google.com> <7af02ceb-563a-4bad-84ee-620aaa513bed@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7af02ceb-563a-4bad-84ee-620aaa513bed@redhat.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251006_061748_732801_EF834CA8 X-CRM114-Status: GOOD ( 23.96 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Oct 06, 2025 at 09:55:27AM +0200, David Hildenbrand wrote: > > > Modules linked in: > > > CPU: 1 UID: 0 PID: 25189 Comm: syz.2.7336 Not tainted syzkaller #0 PREEMPT > > > Hardware name: linux,dummy-virt (DT) > > > pstate: 00402009 (nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) > > > pc : copy_highpage+0x150/0x334 arch/arm64/mm/copypage.c:55 > > > lr : copy_highpage+0xb4/0x334 arch/arm64/mm/copypage.c:25 > > > sp : ffff800088053940 > > > x29: ffff800088053940 x28: ffffc1ffc0acf800 x27: ffff800088053b10 > > > x26: ffffc1ffc0acf808 x25: ffffc1ffc037b1c0 x24: ffffc1ffc037b1c0 > > > x23: ffffc1ffc0acf800 x22: ffffc1ffc0acf800 x21: fff000002b3e0000 > > > x20: fff000000dec7000 x19: ffffc1ffc037b1c0 x18: 0000000000000000 > > > x17: fff07ffffcffa000 x16: ffff800080008000 x15: 0000000000000001 > > > x14: 0000000000000000 x13: 0000000000000003 x12: 000000000006d9ad > > > x11: 0000000000000000 x10: 0000000000000010 x9 : 0000000000000000 > > > x8 : 0000000000000000 x7 : 0000000000000000 x6 : 0000000000000000 > > > x5 : ffff800088053b18 x4 : ffff80008032df94 x3 : 00000000ff000000 > > > x2 : 01ffc00003000001 x1 : 01ffc00003000001 x0 : 01ffc00003000001 > > > Call trace: > > > try_page_mte_tagging arch/arm64/include/asm/mte.h:93 [inline] (P) > > > copy_highpage+0x150/0x334 arch/arm64/mm/copypage.c:55 (P) > > > copy_mc_highpage include/linux/highmem.h:383 [inline] > > > folio_mc_copy+0x44/0x6c mm/util.c:740 > > > __migrate_folio.constprop.0+0xc4/0x23c mm/migrate.c:851 > > > migrate_folio+0x1c/0x2c mm/migrate.c:882 > > > move_to_new_folio+0x58/0x144 mm/migrate.c:1097 > > > migrate_folio_move mm/migrate.c:1370 [inline] > > > migrate_folios_move mm/migrate.c:1719 [inline] > > > migrate_pages_batch+0xaf4/0x1024 mm/migrate.c:1966 > > > migrate_pages_sync mm/migrate.c:2023 [inline] > > > migrate_pages+0xb9c/0xcdc mm/migrate.c:2105 > > > do_mbind+0x20c/0x4a4 mm/mempolicy.c:1539 > > > kernel_mbind mm/mempolicy.c:1682 [inline] > > > __do_sys_mbind mm/mempolicy.c:1756 [inline] > > > > I don't think we ever stressed MTE with mbind before. I have a suspicion > > this problem has been around for some time. > > > > My reading of do_mbind() is that it ends up allocating pages for > > migrating into via alloc_migration_target_by_mpol() -> > > folio_alloc_mpol(). Pages returned should be untagged and uninitialised > > unless the PG_* flags have not been cleared on a prior free. Or > > migrate_pages_batch() somehow reuses some pages instead of reallocating. > > Staring at __migrate_folio(), I assume we can end up successfully calling > folio_mc_copy(), but then failing in __folio_migrate_mapping(). > > Seems to be as easy as failing the folio_ref_freeze() in > __folio_migrate_mapping(). > > We return -EAGAIN in that case, making the caller retry, stumbling into an > already-tagged page. (with the same source / destination parameters) IIRC) > > So likely this is simply us re-doing the copy after a migration failed after > the copy. > > Could it happen that we are calling it with a different source/destination > combination the second time? I don't think so, but I am not 100% sure. Thanks David. I can now see how it would retry on the same pages without reallocating. At least we know it's not causing any side-effects, only messing up the MTE safety warnings. > The most reliable way would be to un-tag in case folio_mc_copy succeeded but > __folio_migrate_mapping() failed. Clearing an MTE specific flag in the core code doesn't look great. Also going for some generic mask like PAGE_FLAGS_CHECK_AT_PREP may have side-effects as we don't know where the page is coming from (we have those get_new_folio()/put_new_folio() arguments passed on by higher up callers). I'm tempted to just drop the warning in the arm64 copy_highpage(), replace it with a comment about migration retrying on a potentially tagged page. It will have to override the tags each time (as it currently does but also warns). -- Catalin