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([2a01:599:904:96e0:a245:aa9f:6c57:eb41]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-438dcc6df36sm53447555e9.25.2025.01.30.00.56.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 30 Jan 2025 00:56:22 -0800 (PST) Message-ID: Date: Thu, 30 Jan 2025 09:56:20 +0100 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 01/12] mm/gup: reject FOLL_SPLIT_PMD with hugetlb VMAs To: John Hubbard , linux-kernel@vger.kernel.org Cc: linux-doc@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-mm@kvack.org, nouveau@lists.freedesktop.org, Andrew Morton , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Jonathan Corbet , Alex Shi , Yanteng Si , Karol Herbst , Lyude Paul , Danilo Krummrich , David Airlie , Simona Vetter , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , Pasha Tatashin , Peter Xu , Alistair Popple , Jason Gunthorpe , stable@vger.kernel.org References: <20250129115411.2077152-1-david@redhat.com> <20250129115411.2077152-2-david@redhat.com> <24e88fec-65b5-47ad-8833-67257f86fde5@nvidia.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: <24e88fec-65b5-47ad-8833-67257f86fde5@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 29.01.25 22:42, John Hubbard wrote: > On 1/29/25 3:53 AM, David Hildenbrand wrote: >> We only have two FOLL_SPLIT_PMD users. While uprobe refuses hugetlb >> early, make_device_exclusive_range() can end up getting called on >> hugetlb VMAs. >> >> Right now, this means that with a PMD-sized hugetlb page, we can end >> up calling split_huge_pmd(), because pmd_trans_huge() also succeeds >> with hugetlb PMDs. >> >> For example, using a modified hmm-test selftest one can trigger: >> >> [ 207.017134][T14945] ------------[ cut here ]------------ >> [ 207.018614][T14945] kernel BUG at mm/page_table_check.c:87! >> [ 207.019716][T14945] Oops: invalid opcode: 0000 [#1] PREEMPT SMP KASAN NOPTI >> [ 207.021072][T14945] CPU: 3 UID: 0 PID: ... >> [ 207.023036][T14945] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-2.fc40 04/01/2014 >> [ 207.024834][T14945] RIP: 0010:page_table_check_clear.part.0+0x488/0x510 >> [ 207.026128][T14945] Code: ... >> [ 207.029965][T14945] RSP: 0018:ffffc9000cb8f348 EFLAGS: 00010293 >> [ 207.031139][T14945] RAX: 0000000000000000 RBX: 00000000ffffffff RCX: ffffffff8249a0cd >> [ 207.032649][T14945] RDX: ffff88811e883c80 RSI: ffffffff8249a357 RDI: ffff88811e883c80 >> [ 207.034183][T14945] RBP: ffff888105c0a050 R08: 0000000000000005 R09: 0000000000000000 >> [ 207.035688][T14945] R10: 00000000ffffffff R11: 0000000000000003 R12: 0000000000000001 >> [ 207.037203][T14945] R13: 0000000000000200 R14: 0000000000000001 R15: dffffc0000000000 >> [ 207.038711][T14945] FS: 00007f2783275740(0000) GS:ffff8881f4980000(0000) knlGS:0000000000000000 >> [ 207.040407][T14945] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> [ 207.041660][T14945] CR2: 00007f2782c00000 CR3: 0000000132356000 CR4: 0000000000750ef0 >> [ 207.043196][T14945] PKRU: 55555554 >> [ 207.043880][T14945] Call Trace: >> [ 207.044506][T14945] >> [ 207.045086][T14945] ? __die+0x51/0x92 >> [ 207.045864][T14945] ? die+0x29/0x50 >> [ 207.046596][T14945] ? do_trap+0x250/0x320 >> [ 207.047430][T14945] ? do_error_trap+0xe7/0x220 >> [ 207.048346][T14945] ? page_table_check_clear.part.0+0x488/0x510 >> [ 207.049535][T14945] ? handle_invalid_op+0x34/0x40 >> [ 207.050494][T14945] ? page_table_check_clear.part.0+0x488/0x510 >> [ 207.051681][T14945] ? exc_invalid_op+0x2e/0x50 >> [ 207.052589][T14945] ? asm_exc_invalid_op+0x1a/0x20 >> [ 207.053596][T14945] ? page_table_check_clear.part.0+0x1fd/0x510 >> [ 207.054790][T14945] ? page_table_check_clear.part.0+0x487/0x510 >> [ 207.055993][T14945] ? page_table_check_clear.part.0+0x488/0x510 >> [ 207.057195][T14945] ? page_table_check_clear.part.0+0x487/0x510 >> [ 207.058384][T14945] __page_table_check_pmd_clear+0x34b/0x5a0 >> [ 207.059524][T14945] ? __pfx___page_table_check_pmd_clear+0x10/0x10 >> [ 207.060775][T14945] ? __pfx___mutex_unlock_slowpath+0x10/0x10 >> [ 207.061940][T14945] ? __pfx___lock_acquire+0x10/0x10 >> [ 207.062967][T14945] pmdp_huge_clear_flush+0x279/0x360 >> [ 207.064024][T14945] split_huge_pmd_locked+0x82b/0x3750 >> ... >> >> Before commit 9cb28da54643 ("mm/gup: handle hugetlb in the generic >> follow_page_mask code"), we would have ignored the flag; instead, let's > > ...and so after that commit (which doesn't touch FOLL_SPLIT_PMD, we no > longer ignore the flag? At a first look at that commit, I don't quite > understand the connection, can you clarify just a bit for me? Sure! Before that commit we always went via hugetlb_follow_page_mask(), so we never ended up in follow_pmd_mask(). hugetlb_follow_page_mask() didn't check for the flag ("ignored it"), so we would not have crashed in GUP. Thanks! -- Cheers, David / dhildenb