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]) by smtp.lore.kernel.org (Postfix) with ESMTP id 136A6C6FD1F for ; Tue, 2 Apr 2024 16:18:45 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 556B96B0089; Tue, 2 Apr 2024 12:18:45 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 506C26B008A; Tue, 2 Apr 2024 12:18:45 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3A6826B008C; Tue, 2 Apr 2024 12:18:45 -0400 (EDT) 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 1BD666B0089 for ; Tue, 2 Apr 2024 12:18:45 -0400 (EDT) Received: from smtpin29.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id AD59B120934 for ; Tue, 2 Apr 2024 16:18:43 +0000 (UTC) X-FDA: 81965100126.29.E73E650 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf25.hostedemail.com (Postfix) with ESMTP id 894EEA000A for ; Tue, 2 Apr 2024 16:18:41 +0000 (UTC) Authentication-Results: imf25.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf25.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1712074722; 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-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=d0viNxp0he/g5Z5V2R8ONvqxfBBjawxRkarzbfC2uR4=; b=0/2nLVhL/ETmM4hVd1GkM/36RiFhFP+z0FfLLnTKZCFcuIhlFDD8yp5aIDilAj8b+3P2pi D55mGYMpYRKAePKImF+nW0ALaNy6DosLLtj2wemWq8ij8aeH2FlgOKU54slhqS9RBv3M/M wM9ZzwnWNalHj8Ws0U9rvmUdILk08Z8= ARC-Authentication-Results: i=1; imf25.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf25.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1712074722; a=rsa-sha256; cv=none; b=VVF0mKEiadkg7EiyEX5Q2AfUcbuM/OMTE1m39fyQA3Yg6WpYDeHioZal0YtSUp9wqLWqMR /IwMsaRny0tDc6cb7+244yZMW8N3tu45RibpMO5S4XVZk4u0TK4F/NV9pzCim3dat1gh0R pYIHSvbdTUBTAhlBmKbHpuPwU8QJV9A= 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 BA6C61007; Tue, 2 Apr 2024 09:19:11 -0700 (PDT) Received: from [10.1.38.163] (XHFQ2J9959.cambridge.arm.com [10.1.38.163]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 4D35D3F64C; Tue, 2 Apr 2024 09:18:37 -0700 (PDT) Message-ID: <3f670f03-ee97-4368-94ca-e8d18a1b1a69@arm.com> Date: Tue, 2 Apr 2024 17:18:36 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 13/13] mm/gup: Handle hugetlb in the generic follow_page_mask code Content-Language: en-GB To: Matthew Wilcox , David Hildenbrand Cc: peterx@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Yang Shi , "Kirill A . Shutemov" , Mike Kravetz , John Hubbard , Michael Ellerman , Andrew Jones , Muchun Song , linux-riscv@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, Christophe Leroy , Andrew Morton , Christoph Hellwig , Lorenzo Stoakes , Rik van Riel , linux-arm-kernel@lists.infradead.org, Andrea Arcangeli , "Aneesh Kumar K . V" , Vlastimil Babka , James Houghton , Jason Gunthorpe , Mike Rapoport , Axel Rasmussen References: <20240327152332.950956-1-peterx@redhat.com> <20240327152332.950956-14-peterx@redhat.com> <5d9dd9a7-e544-4741-944c-469b79c2c649@redhat.com> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: mykduuupu8uchbw1dujj8h4gqpsopqn9 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 894EEA000A X-HE-Tag: 1712074721-527506 X-HE-Meta: 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 87J6GatH Rpj119DqsKBCaCx7b/7rlna2l0KehK0rnwkmdoiJWmftn4v5KlyFBPCtQYX73bvnycfNZcqRtHRpW6k4+2lF0fTo0f6Ks9YKMjQClWcHDGxCyoA4TEkZkB7x2evFEAPJSaJSWcyggREjCe2mnM/sBLJ15/xTh+ZhefZKmWeBUhGhfDcRbJy44dW1PZaWQYzdmfqXB X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 02/04/2024 17:00, Matthew Wilcox wrote: > On Tue, Apr 02, 2024 at 05:26:28PM +0200, David Hildenbrand wrote: >>> The oops trigger is at mm/gup.c:778: >>> VM_BUG_ON_PAGE(!PageHead(page) && !is_zone_device_page(page), page); >>> >>> So 2M passed ok, and its failing for 32M, which is cont-pmd. I'm guessing you're trying to iterate 2M into a cont-pmd folio and ending up with an unexpected tail page? >> >> I assume we find the expected tail page, it's just that the check >> >> VM_BUG_ON_PAGE(!PageHead(page) && !is_zone_device_page(page), page); >> >> Doesn't make sense with hugetlb folios. We might have a tail page mapped in >> a cont-pmd entry. As soon as we call follow_huge_pmd() on "not the first >> cont-pmd entry", we trigger this check. >> >> Likely this sanity check must also allow for hugetlb folios. Or we should >> just remove it completely. >> >> In the past, we wanted to make sure that we never get tail pages of THP from >> PMD entries, because something would currently be broken (we don't support >> THP > PMD). > > That was a practical limitation on my part. We have various parts of > the MM which assume that pmd_page() returns a head page and until we > get all of those fixed, adding support for folios larger than PMD_SIZE > was only going to cause trouble for no significant wins. > > I agree with you we should get rid of this assertion entirely. We should > fix all the places which assume that pmd_page() returns a head page, > but that may take some time. > > As an example, filemap_map_pmd() has: > > if (pmd_none(*vmf->pmd) && folio_test_pmd_mappable(folio)) { > struct page *page = folio_file_page(folio, start); > vm_fault_t ret = do_set_pmd(vmf, page); > > and then do_set_pmd() has: > > if (page != &folio->page || folio_order(folio) != HPAGE_PMD_ORDER) > return ret; > > so we'd simply refuse to use a PMD to map a folio larger than PMD_SIZE. > There's a lot of work to be done to make this work generally (not to > mention figuring out how to handle mapcount for such folios ;-). > > This particular case seems straightforward though. Just remove the > assertion. Removing the assertion gets me further, but then I end up with this: [ 9.748422] kernel BUG at include/linux/page-flags.h:1098! [ 9.748897] Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP [ 9.749590] Modules linked in: [ 9.749867] CPU: 2 PID: 1155 Comm: gup_longterm Not tainted 6.9.0-rc2-00210-g910ff1a347e4-dirty #12 [ 9.750682] Hardware name: linux,dummy-virt (DT) [ 9.751095] pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) [ 9.751729] pc : follow_page_mask+0x730/0x850 [ 9.752152] lr : follow_page_mask+0x730/0x850 [ 9.752573] sp : ffff8000898f3aa0 [ 9.752882] x29: ffff8000898f3aa0 x28: fffffdffc52b91a8 x27: 0000000000000001 [ 9.753543] x26: ffff00014ae46d08 x25: 00003c0005d88000 x24: fffffdffc5d88000 [ 9.754221] x23: ffffc1ffc0000000 x22: 0000000000080101 x21: ffff8000898f3ba8 [ 9.754875] x20: 0000fffff4200000 x19: ffff0001a3d64450 x18: 0000000000000010 [ 9.755567] x17: 2864616548656761 x16: 5021202626202965 x15: 6761702865677548 [ 9.756254] x14: 6567615028454741 x13: 2929656761702864 x12: 6165486567615021 [ 9.756953] x11: 2026262029656761 x10: ffffaaac08f1d6e0 x9 : ffffaaac0612f090 [ 9.757671] x8 : 00000000ffffefff x7 : ffffaaac08f1d6e0 x6 : 0000000000000000 [ 9.758356] x5 : ffff00017ffb9cc8 x4 : 0000000000000fff x3 : 0000000000000000 [ 9.758983] x2 : 0000000000000000 x1 : ffff000189ecb480 x0 : 0000000000000046 [ 9.759663] Call trace: [ 9.759901] follow_page_mask+0x730/0x850 [ 9.760293] __get_user_pages+0xf4/0x3e8 [ 9.760683] __gup_longterm_locked+0x204/0xa70 [ 9.761110] pin_user_pages+0x88/0xc0 [ 9.761486] gup_test_ioctl+0x860/0xc40 [ 9.761866] __arm64_sys_ioctl+0xb0/0x100 [ 9.762254] invoke_syscall+0x50/0x128 [ 9.762630] el0_svc_common.constprop.0+0x48/0xf8 [ 9.763104] do_el0_svc+0x28/0x40 [ 9.763413] el0_svc+0x34/0xe0 [ 9.763699] el0t_64_sync_handler+0x13c/0x158 [ 9.764139] el0t_64_sync+0x190/0x198 [ 9.764465] Code: aa1803e0 d000d8e1 911d6021 97fff4c9 (d4210000) [ 9.765053] ---[ end trace 0000000000000000 ]--- [ 9.765520] note: gup_longterm[1155] exited with irqs disabled [ 9.766146] note: gup_longterm[1155] exited with preempt_count 2 [ 9.767366] ------------[ cut here ]------------ [ 9.768062] WARNING: CPU: 2 PID: 0 at kernel/context_tracking.c:128 ct_kernel_exit.constprop.0+0x108/0x120 [ 9.769146] Modules linked in: [ 9.769429] CPU: 2 PID: 0 Comm: swapper/2 Tainted: G D 6.9.0-rc2-00210-g910ff1a347e4-dirty #12 [ 9.770338] Hardware name: linux,dummy-virt (DT) [ 9.770837] pstate: 204003c5 (nzCv DAIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--) [ 9.771615] pc : ct_kernel_exit.constprop.0+0x108/0x120 [ 9.772150] lr : ct_idle_enter+0x10/0x20 [ 9.772539] sp : ffff8000801b3dc0 [ 9.772913] x29: ffff8000801b3dc0 x28: 0000000000000000 x27: 0000000000000000 [ 9.773769] x26: 0000000000000000 x25: ffff00014149e900 x24: 0000000000000000 [ 9.774526] x23: 0000000000000000 x22: ffffaaac08e99d48 x21: ffffaaac08385730 [ 9.775255] x20: ffffaaac08e99c28 x19: ffff00017ffc8da0 x18: 0000fffff5ffffff [ 9.775924] x17: 0000000000000000 x16: 1fffe0002a57c9e1 x15: 0000000000000001 [ 9.776619] x14: ffffffffffffffff x13: 0000000000000000 x12: ffffaaac07a06968 [ 9.777246] x11: 000000ae44c42eec x10: 0000000000000ad0 x9 : ffffaaac06189230 [ 9.777942] x8 : ffff00014149f430 x7 : 02c9acb509db422c x6 : 000000001015a9f0 [ 9.778635] x5 : 4000000000000002 x4 : ffff555577c46000 x3 : ffff8000801b3dc0 [ 9.779671] x2 : ffffaaac08382da0 x1 : 4000000000000000 x0 : ffffaaac08382da0 [ 9.780703] Call trace: [ 9.781150] ct_kernel_exit.constprop.0+0x108/0x120 [ 9.781949] ct_idle_enter+0x10/0x20 [ 9.782246] default_idle_call+0x3c/0x160 [ 9.782624] do_idle+0x21c/0x280 [ 9.782945] cpu_startup_entry+0x3c/0x50 [ 9.783268] secondary_start_kernel+0x140/0x168 [ 9.783818] __secondary_switched+0xb8/0xc0 [ 9.784163] ---[ end trace 0000000000000000 ]--- Which is caused by this: static __always_inline int PageAnonExclusive(const struct page *page) { VM_BUG_ON_PGFLAGS(!PageAnon(page), page); VM_BUG_ON_PGFLAGS(PageHuge(page) && !PageHead(page), page); <<<< return test_bit(PG_anon_exclusive, &PF_ANY(page, 1)->flags); } Which is called from can_follow_write_pmd(), called just after the assert I just commented out. It's triggered by this test: # [RUN] R/W longterm GUP pin in MAP_PRIVATE file mapping ... with memfd hugetlb (32768 kB) Which is the first MAP_PRIVATE test for cont-pmd mapped hugetlb. (All MAP_SHARED tests are passing). Looks like can_follow_write_pmd() returns early for VM_SHARED mappings. I don't think we only keep the PAE flag in the head page for hugetlb pages? So we can't just remove this assert? I tried just commenting it out and get assert further down follow_huge_pmd(): VM_BUG_ON_PAGE((flags & FOLL_PIN) && PageAnon(page) && !PageAnonExclusive(page), page); Thanks, Ryan