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(p200300d82f4efd008e13e3b590c81159.dip0.t-ipconnect.de. [2003:d8:2f4e:fd00:8e13:e3b5:90c8:1159]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a6d117bfd9sm10346368f8f.57.2025.06.23.12.19.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 23 Jun 2025 12:19:54 -0700 (PDT) Message-ID: <155d1f58-6568-4efa-968e-af3873707ad0@redhat.com> Date: Mon, 23 Jun 2025 21:19:53 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC 03/14] mm: compare pfns only if the entry is present when inserting pfns/pages To: Pedro Falcato Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, nvdimm@lists.linux.dev, Andrew Morton , Juergen Gross , Stefano Stabellini , Oleksandr Tyshchenko , Dan Williams , Alistair Popple , Matthew Wilcox , Jan Kara , Alexander Viro , Christian Brauner , Zi Yan , Baolin Wang , Lorenzo Stoakes , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Jann Horn References: <20250617154345.2494405-1-david@redhat.com> <20250617154345.2494405-4-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: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: fUDRau4MmvVhxiwDhAU3QtaAbHEQK7owPHX7qHq0mR4_1750706396 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 0F65140016 X-Rspamd-Server: rspam10 X-Stat-Signature: efhboptzx9djzop69uh7jo8hj39txsiq X-HE-Tag: 1750706399-906701 X-HE-Meta: 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 Qc6E2tEq kCxlpVie8Iy+OKKHRfsz5W4W/fUfQ+2FXQCwxlu+Vcv8MlHxcxAE/UQgP1+yQMwKFEGgnEVaBRRvmLoURWrhT4ZhrrtC/oiPy6jvjy8Ph+oA/JusrJ4u212IvXAg3vQHMqKU64TiLX6mrFisl0hgAYQGJTKImCqdNfEUSTTKjguHT0EtUtR6gh0I5tZzZevqdR5kTc+p70IjvhPyd54ny80kowDYid5Izhe4r3kop70lT5Zd1gNnZ6DlzMb65D+as1cwng0WusGO4zgOjp2vqv8jN0pgOr81qOnB9JWQE4cyI2VwemsY4jr2nRr8Xu/zSKK/Z/X7HGpJtVu4MLCfsv76qCyzfYfPr8QEyDOW//wlCOHnrvAsVDe5qXd25L4PPqJTkPxdZ60nav4+hTAPMwq0z3g== 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 20.06.25 20:24, Pedro Falcato wrote: > On Tue, Jun 17, 2025 at 05:43:34PM +0200, David Hildenbrand wrote: >> Doing a pte_pfn() etc. of something that is not a present page table >> entry is wrong. Let's check in all relevant cases where we want to >> upgrade write permissions when inserting pfns/pages whether the entry >> is actually present. >> >> It's not expected to have caused real harm in practice, so this is more a >> cleanup than a fix for something that would likely trigger in some >> weird circumstances. > > Couldn't we e.g have a swap entry's "pfn" accidentally match the one we're > inserting? Isn't that a correctness problem? In theory yes, in practice I think this will not happen. ... especially because the WARN_ON_ONCE() would already trigger in many other cases before we would find one situation where it doesn't. That's why I decided against Fixes: and declaring this more a cleanup, because the starts really would have to align ... :) Thanks! -- Cheers, David / dhildenb