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Peter Anvin" , Linus Torvalds References: <20250422144942.2871395-1-david@redhat.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: <20250422144942.2871395-1-david@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: ajpg0SOzCDQ4NbfKBD1jpBO4yhHIM6FUo58PN_5kUWU_1745333696 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: 2863FA000C X-Stat-Signature: tqhzxfe8e7bjdfr3ucbpjtp9gfudbaf9 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1745333700-81794 X-HE-Meta: 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 OY6RWk5J amic4biwjElYXjjXUCy4rpy+CoyN5sv9z8knNKsQ9V0K6euTJunB2CUbhJtmK8DvotMlV7bMh3mxzKieYYEgWzfFqbTJzHrb5i7H6vFV28VP1RRuhomsdONyLWzYrt7aLtQDjx8M/Ja1u3obBaWVjbSQOb5YADO7sVyZ/Av3HkibOBdgIYch2YByuZyWi50J2npt0PTtLILwzNdrzsZUFezVXp1iCvmJFgih/AVqEXcOAzrhahRnFAZl0/8t0OQPj/SGb3qtEI38H5jHrmEIVfTM5omi7nI1uSo5rrFpa++BXofPKJFOZnwFAqdw3uATmA6IKNjf8sR+dVHVMmNR2xB547J67I+HK/jNSpW+UunCUrRII1I8GeabLPEmnER7DRsLmqF+IqoUdem6ZNuqaWy2ERWa9L5xu8bETQ1UxVmXjOWL/QiSlUKrdvAF5jEcZp0t92u8KA80IhBM= 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 22.04.25 16:49, David Hildenbrand wrote: > Not intuitive, but vm_area_dup() located in kernel/fork.c is not only > used for duplicating VMAs during fork(), but also for duplicating VMAs > when splitting VMAs or when mremap()'ing them. > > VM_PFNMAP mappings can at least get ordinarily mremap()'ed (no change in > size) and apparently also shrunk during mremap(), which implies > duplicating the VMA in __split_vma() first. > > In case of ordinary mremap() (no change in size), we first duplicate the > VMA in copy_vma_and_data()->copy_vma() to then call untrack_pfn_clear() on > the old VMA: we effectively move the VM_PAT reservation. So the > untrack_pfn_clear() call on the new VMA duplicating is wrong in that > context. > > Splitting of VMAs seems problematic, because we don't duplicate/adjust the > reservation when splitting the VMA. Instead, in memtype_erase() -- called > during zapping/munmap -- we shrink a reservation in case only the end > address matches: Assume we split a VMA into A and B, both would share a > reservation until B is unmapped. > > So when unmapping B, the reservation would be updated to cover only A. When > unmapping A, we would properly remove the now-shrunk reservation. That > scenario describes the mremap() shrinking (old_size > new_size), where > we split + unmap B, and the untrack_pfn_clear() on the new VMA when > is wrong. > > What if we manage to split a VM_PFNMAP VMA into A and B and unmap A > first? It would be broken because we would never free the reservation. > Likely, there are ways to trigger such a VMA split outside of mremap(). As expected ... with a simple reproducer that uses mprotect() to split such a VMA I can trigger x86/PAT: pat_mremap:26448 freeing invalid memtype [mem 0x00000000-0x00000fff] -- Cheers, David / dhildenb