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[2003:cb:c74b:d000:3a9:de5c:9ae6:ccb3]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4313f56ea10sm47224315e9.24.2024.10.16.04.05.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 16 Oct 2024 04:05:55 -0700 (PDT) Message-ID: <0436c217-0afc-45e6-949b-2291ee1ebc6e@redhat.com> Date: Wed, 16 Oct 2024 13:05:54 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1] mm/pagewalk: fix usage of pmd_leaf()/pud_leaf() without present check To: Qi Zheng Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, syzbot+7d917f67c05066cec295@syzkaller.appspotmail.com, Andrew Morton , Jann Horn References: <20241015111236.1290921-1-david@redhat.com> <4898fdf4-7c88-4697-9df4-64fd8a900e95@redhat.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 16.10.24 12:58, Qi Zheng wrote: > > > On 2024/10/15 21:13, David Hildenbrand wrote: >> On 15.10.24 13:12, David Hildenbrand wrote: >>> pmd_leaf()/pud_leaf() only implies a pmd_present()/pud_present() check on >>> some architectures. We really should check for >>> pmd_present()/pud_present() first. >>> >>> This should explain the report we got on ppc64 (which has >>> CONFIG_PGTABLE_HAS_HUGE_LEAVES set in the config) that triggered: >>>     VM_WARN_ON_ONCE(pmd_leaf(pmdp_get_lockless(pmdp))); >>> >>> Likely we had a PMD migration entry for which pmd_leaf() did not >>> trigger. We raced with restoring the PMD migration entry, and suddenly >>> saw a pmd_leaf(). In this case, pte_offset_map_lock() saved us from more >>> trouble, because it rechecks the PMD value, but we would not have >>> processed >>> the migration entry -- which is not too bad because the only user of >>> FW_MIGRATION is KSM for unsharing, and KSM only applies to small folios. >>> >>> Further, we shouldn't re-read the PMD/PUD value for our warning, the >>> primary purpose of the VM_WARN_ON_ONCE() is to find spurious use of >>> pmd_leaf()/pud_leaf() without CONFIG_PGTABLE_HAS_HUGE_LEAVES. >>> >>> As a side note, we are currently not implementing FW_MIGRATION support >>> for PUD migration entries, which likely should exist due to hugetlb. Add >>> a TODO so this won't fall through the cracks if more FW_MIGRATION users >>> get added. >>> >>> Fixes: aa39ca6940f1 ("mm/pagewalk: introduce folio_walk_start() + >>> folio_walk_end()") >>> Reported-by: syzbot+7d917f67c05066cec295@syzkaller.appspotmail.com >>> Closes: >>> https://lkml.kernel.org/r/670d3248.050a0220.3e960.0064.GAE@google.com >>> Cc: Andrew Morton >>> Cc: Jann Horn >>> Signed-off-by: David Hildenbrand >>> --- >> >> Was able to write a quick reproducer and verify that the issue no longer >> triggers with this fix. >> >> https://gitlab.com/davidhildenbrand/scratchspace/-/blob/main/reproducers/move-pages-pmd-leaf.c >> >> Without this fix after a couple of seconds in a VM with 2 NUMA nodes: >> >> [   54.333753] ------------[ cut here ]------------ >> [   54.334901] WARNING: CPU: 20 PID: 1704 at mm/pagewalk.c:815 >> folio_walk_start+0x48f/0x6e0 >> [   54.336455] Modules linked in: ... >> [   54.345009] CPU: 20 UID: 0 PID: 1704 Comm: move-pages-pmd- Not >> tainted 6.12.0-rc2+ #81 >> [   54.346529] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS >> 1.16.3-2.fc40 04/01/2014 >> [   54.348191] RIP: 0010:folio_walk_start+0x48f/0x6e0 >> [   54.349134] Code: b5 ad 48 8d 35 00 00 00 00 e8 6d 59 d7 ff e8 08 74 >> da ff e9 9c fe ff ff 4c 8b 7c 24 08 4c 89 ff e8 26 2b be 00 e9 8a fe ff >> ff <0f> 0b e9 ec fe ff ff f7 c2 ff 0f 00 00 0f 85 81 fe ff ff 48 8b 02 >> [   54.352660] RSP: 0018:ffffb7e4c430bc78 EFLAGS: 00010282 >> [   54.353679] RAX: 80000002a3e008e7 RBX: ffff9946039aa580 RCX: >> ffff994380000000 >> [   54.355056] RDX: ffff994606aec000 RSI: 00007f004b000000 RDI: >> 0000000000000000 >> [   54.356440] RBP: 00007f004b000000 R08: 0000000000000591 R09: >> 0000000000000001 >> [   54.357820] R10: 0000000000000200 R11: 0000000000000001 R12: >> ffffb7e4c430bd10 >> [   54.359198] R13: ffff994606aec2c0 R14: 0000000000000002 R15: >> ffff994604a89b00 >> [   54.360564] FS:  00007f004ae006c0(0000) GS:ffff9947f7400000(0000) >> knlGS:0000000000000000 >> [   54.362111] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> [   54.363242] CR2: 00007f004adffe58 CR3: 0000000281e12005 CR4: >> 0000000000770ef0 >> [   54.364615] PKRU: 55555554 >> [   54.365153] Call Trace: >> [   54.365646]  >> [   54.366073]  ? __warn.cold+0xb7/0x14d >> [   54.366796]  ? folio_walk_start+0x48f/0x6e0 >> [   54.367628]  ? report_bug+0xff/0x140 >> [   54.368324]  ? handle_bug+0x58/0x90 >> [   54.369019]  ? exc_invalid_op+0x17/0x70 >> [   54.369771]  ? asm_exc_invalid_op+0x1a/0x20 >> [   54.370606]  ? folio_walk_start+0x48f/0x6e0 >> [   54.371415]  ? folio_walk_start+0x9e/0x6e0 >> [   54.372227]  do_pages_move+0x1c5/0x680 >> [   54.372972]  kernel_move_pages+0x1a1/0x2b0 >> [   54.373804]  __x64_sys_move_pages+0x25/0x30 > > It would be better to add this call stack to the commit message, which > can help people find this fix patch when they encounter same problem. ;) The commit is not part of a released kernel, though, and a lore search would return the result until it's included. Before it's included, the commit message won't really be helpful :) But sure, @Andrew, can we include that in the commit? > > Otherwise, LGTM. > > Acked-by: Qi Zheng > Thanks! -- Cheers, David / dhildenb