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[2003:cb:c707:7600:5c18:5a7d:c5b7:e7a9]) by smtp.gmail.com with ESMTPSA id a20-20020a05600c225400b00410df4bf22esm15060125wmm.38.2024.02.27.05.00.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 27 Feb 2024 05:00:10 -0800 (PST) Message-ID: Date: Tue, 27 Feb 2024 14:00:09 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [Question] CoW on VM_PFNMAP vma during write fault To: Wupeng Ma , akpm@linux-foundation.org, khlebnikov@openvz.org, jaredeh@gmail.com, linmiaohe@huawei.com, hpa@zytor.com Cc: dave.hansen@linux.intel.com, luto@kernel.org, tglx@linutronix.de, peterz@infradead.org, linux-kernel@vger.kernel.org, x86@kernel.org, mingo@redhat.com, rdunlap@infradead.org, bhelgaas@google.com, linux-mm@kvack.org References: <20240227122814.3781907-1-mawupeng1@huawei.com> From: David Hildenbrand 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: <20240227122814.3781907-1-mawupeng1@huawei.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 6955310002A X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: n1ourgefkbqppk1iggkuhkz5igfrqw36 X-HE-Tag: 1709038815-379220 X-HE-Meta: U2FsdGVkX19nJaJFAJWrvzOYCH+/WzcUqI2fPqTC2chResYlgI3jvCFUGZbbMe4WN7czd1GiF3OjIFZMCKcYWhdSC6N7VJ9yGb2iCtnqdO/brV+xKPdNvPxApxI2kU4FtiJYjnHa7g76dmtnLzuie3nXq/T3bMSHz1IZw6Zoh0s7DMF0jyW99l35fnZEP1St3jcd28L3OdaUA/S9JD4dB8/LGyJ3K2Ja+j9Xkp/1LuR0q3LNQaaF0nxSEnoC27nrs2wL7GoXQe/9KTDEjFa12I1F6razAeFKqAQH79bPh09wyjXfhiOO8JC5GT/tQVHcU0WjQg3TmBrZHMXKh4nPZpoJrDDcZ7TpxHPbdCmZU3Nflx9x4wGkkI4XmXoXj0ljNwIGF4gT5k6AqkTJi1/itzVyeEwM5W1eAK3MPp8/evlSwMyek34yfuOpH6+4VZkxjJOjpt0BzHaFa+DkRgaf1WKXllcP6WtOwM1GXiHWMpzqmT4nH23EGNXaDd3bcEExf6Ez/vf6PoYxF22qq6GjwQ/LbVxXJoJumglcAQJu1FHs80+8PYNXOCjGrYK2AaVY/3VkZJPc0sfMskBV2QwXYL2UFcK30lEzTIlKaj965d5CB6tNyZMlhQZozwqgK/gE23+uYnqQCEMteUe9/DDQ7MzXdKfT6Mo/GZr+HGLjRhJWrjUWS5z9a8CzHyvORD1dJ0D58AGxUMQIq0f4j9PTLRaTbygnb709d37grmWTzYuic/JiYsg3WeKJQunqJTLkPPey+T8k1YrqgtMHleCfO3SZXQVv5ZUCK1IX6r/+nOav+p1axTWIrlfbQnOLv40WTUm9Nxb++gGxoTRgme8EGWpiIM+pJg5JqCwRLXkhUK/NmtpsJUaCC3Au0FT/uO8fl3xl3tGjfeP6Lmwp+uG1DxN/d5H7Leq7wtOnb0JEByQ/ncqUlwF2Hb1P88wVaPmJdLRo3jU/TbsJCsC3ptR kNCBi/qN IoGR9YrdHlSK/bLhWEaecGsyNDtLjdYNomeiGDAFGIqJlBlnUazPMA95mJpfUQky+sNcgu3OlssG+/HdUCPuENbXqdEeLwXXwt5aK4h8yANZqV0GYE+v4La98VvciodS09TyhSNhh3iv9ilCJxdcccSZ3SgVp8JPQ/R3if6HW2qp+xhrhVxaLKirfKHk7LrLMvCVq8e74n+Qu2AsRO4MiO0sd6w== 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 27.02.24 13:28, Wupeng Ma wrote: > We find that a warn will be produced during our test, the detail log is > shown in the end. > > The core problem of this warn is that the first pfn of this pfnmap vma is > cleared during memory-failure. Digging into the source we find that this > problem can be triggered as following: > > // mmap with MAP_PRIVATE and specific fd which hook mmap > mmap(MAP_PRIVATE, fd) > __mmap_region > remap_pfn_range > // set vma with pfnmap and the prot of pte is read only > Okay, so we get a MAP_PRIVATE VM_PFNMAP I assume. What fd is that exactly? Often, we disallow private mappings in the mmap() callback (for a good reason). > // memset this memory with trigger fault > handle_mm_fault > __handle_mm_fault > handle_pte_fault > // write fault and !pte_write(entry) > do_wp_page > wp_page_copy // this will alloc a new page with valid page struct > // for this pfnmap vma Here we replace the mapped PFNMAP thingy by a proper anon folio. > > // inject a hwpoison to the first page of this vma I assume this is an anon folio? > madvise_inject_error > memory_failure > hwpoison_user_mappings > try_to_unmap_one > // mark this pte as invalid (hwpoison) > mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm, > address, range.end); > > // during unmap vma, the first pfn of this pfnmap vma is invalid > vm_mmap_pgoff > do_mmap > __do_mmap_mm > __mmap_region > __do_munmap > unmap_region > unmap_vmas > unmap_single_vma > untrack_pfn > follow_phys // pte is already invalidate, WARN_ON here unmap_single_vma()->...->zap_pte_range() should do the right thing when calling vm_normal_page(). untrack_pfn() is the problematic part. > > CoW with a valid page for pfnmap vma is weird to us. Can we use > remap_pfn_range for private vma(read only)? Once CoW happens on a pfnmap > vma during write fault, this page is normal(page flag is valid) for most mm > subsystems, such as memory failure in thais case and extra should be done to > handle this special page. > > During unmap, if this vma is pfnmap, unmap shouldn't be done since page > should not be touched for pfnmap vma. > > But the root problem is that can we insert a valid page for pfnmap vma? > > Any thoughts to solve this warn? vm_normal_page() documentation explains how that magic is supposed to work. vm_normal_page() should be able to correctly identify whether we want to look at the struct page for an anon folio that was COWed. untrack_pfn() indeed does not seem to be well prepared for handling MAP_PRIVATE mappings where we end up having anon folios. I think it will already *completely mess up* simply when unmapping the range without the memory failure involved. See, follow_phys() would get the PFN of the anon folio and then untrack_pfn() would do some nonesense with that. Completely broken. The WARN is just a side-effect of the brokenness. In follow_phys(), we'd likely have to call vm_normal_page(). If we get a page back, we'd likely have to fail follow_phys() instead of returning a PFN of an anon folio. Now, how do we fix untrack_pfn() ? I really don't know. In theory, we might no longer have *any* PFNMAP PFN in there after COW'ing everything. Sounds like MAP_PRIVATE VM_PFNMAP + __HAVE_PFNMAP_TRACKING is some broken garbage (sorry). Can we disallow it? -- Cheers, David / dhildenb