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[2003:cb:c73b:db00:b0d7:66ca:e3e9:6528]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-381c10e7449sm16015220f8f.49.2024.11.05.04.03.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 05 Nov 2024 04:03:52 -0800 (PST) Message-ID: Date: Tue, 5 Nov 2024 13:03:51 +0100 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] mm: Fix __wp_page_copy_user fallback path for remote mm To: Asahi Lina , Andrew Morton Cc: Sergio Lopez Pascual , linux-mm@kvack.org, linux-kernel@vger.kernel.org, asahi@lists.linux.dev References: <20241101-mm-remote-pfn-v1-1-080b609270b7@asahilina.net> 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: <20241101-mm-remote-pfn-v1-1-080b609270b7@asahilina.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 01.11.24 13:08, Asahi Lina wrote: > If the source page is a PFN mapping, we copy back from userspace. > However, if this fault is a remote access, we cannot use > __copy_from_user_inatomic. Instead, use access_remote_vm() in this case. > > Fixes WARN and incorrect zero-filling when writing to CoW mappings in > a remote process, such as when using gdb on a binary present on a DAX > filesystem. > > [ 143.683782] ------------[ cut here ]------------ > [ 143.683784] WARNING: CPU: 1 PID: 350 at mm/memory.c:2904 __wp_page_copy_user+0x120/0x2bc > [ 143.683793] CPU: 1 PID: 350 Comm: gdb Not tainted 6.6.52 #1 > [ 143.683794] Hardware name: linux,dummy-virt (DT) > [ 143.683795] pstate: 61400005 (nZCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--) > [ 143.683796] pc : __wp_page_copy_user+0x120/0x2bc > [ 143.683798] lr : __wp_page_copy_user+0x254/0x2bc > [ 143.683799] sp : ffff80008272b8b0 > [ 143.683799] x29: ffff80008272b8b0 x28: 0000000000000000 x27: ffff000083bad580 > [ 143.683801] x26: 0000000000000000 x25: 0000fffff7fd5000 x24: ffff000081db04c0 > [ 143.683802] x23: ffff00014f24b000 x22: fffffc00053c92c0 x21: ffff000083502150 > [ 143.683803] x20: 0000fffff7fd5000 x19: ffff80008272b9d0 x18: 0000000000000000 > [ 143.683804] x17: ffff000081db0500 x16: ffff800080fe52a0 x15: 0000fffff7fd5000 > [ 143.683804] x14: 0000000000bb1845 x13: 0000000000000080 x12: ffff80008272b880 > [ 143.683805] x11: ffff000081d13600 x10: ffff000081d13608 x9 : ffff000081d1360c > [ 143.683806] x8 : ffff000083a16f00 x7 : 0000000000000010 x6 : ffff00014f24b000 > [ 143.683807] x5 : ffff00014f24c000 x4 : 0000000000000000 x3 : ffff000083582000 > [ 143.683807] x2 : 0000000000000f80 x1 : 0000fffff7fd5000 x0 : 0000000000001000 > [ 143.683808] Call trace: > [ 143.683809] __wp_page_copy_user+0x120/0x2bc > [ 143.683810] wp_page_copy+0x98/0x5c0 > [ 143.683813] do_wp_page+0x250/0x530 > [ 143.683814] __handle_mm_fault+0x278/0x284 > [ 143.683817] handle_mm_fault+0x64/0x1e8 > [ 143.683819] faultin_page+0x5c/0x110 > [ 143.683820] __get_user_pages+0xc8/0x2f4 > [ 143.683821] get_user_pages_remote+0xac/0x30c > [ 143.683823] __access_remote_vm+0xb4/0x368 > [ 143.683824] access_remote_vm+0x10/0x1c > [ 143.683826] mem_rw.isra.0+0xc4/0x218 > [ 143.683831] mem_write+0x18/0x24 > [ 143.683831] vfs_write+0xa0/0x37c > [ 143.683834] ksys_pwrite64+0x7c/0xc0 > [ 143.683834] __arm64_sys_pwrite64+0x20/0x2c > [ 143.683835] invoke_syscall+0x48/0x10c > [ 143.683837] el0_svc_common.constprop.0+0x40/0xe0 > [ 143.683839] do_el0_svc+0x1c/0x28 > [ 143.683841] el0_svc+0x3c/0xdc > [ 143.683846] el0t_64_sync_handler+0x120/0x12c > [ 143.683848] el0t_64_sync+0x194/0x198 > [ 143.683849] ---[ end trace 0000000000000000 ]--- > > Signed-off-by: Asahi Lina > --- > mm/memory.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 3ccee51adfbbd007b24331fe6874265f231a877b..dba25d9734063ac02cdaeb0a5cd5432473f6372e 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -3081,13 +3081,18 @@ static inline int __wp_page_copy_user(struct page *dst, struct page *src, > update_mmu_cache_range(vmf, vma, addr, vmf->pte, 1); > } > > + /* If the mm is a remote mm, copy in the page using access_remote_vm() */ > + if (current->mm != mm) { > + if (access_remote_vm(mm, (unsigned long)uaddr, kaddr, PAGE_SIZE, 0) != PAGE_SIZE) access_remote_vm() will do a mmap_read_lock_killable() and then call into get_user_page_vma_remote() -- fortunately read-access, otherwise we'd be in trouble :) . So we should already be holding the mmap read lock from the previous access_remote_vm() users (who we end up here) ... doesn't this complain with lockdep about recursive locking? I keep forgetting locking rules, so I might just be wrong. -- Cheers, David / dhildenb