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[213.175.37.12]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-42e754a6f82sm158012075e9.37.2024.09.24.05.58.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 24 Sep 2024 05:58:24 -0700 (PDT) Message-ID: <4f9dffe7-a652-4476-ae18-15997085e5b4@redhat.com> Date: Tue, 24 Sep 2024 14:58:23 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 01/13] mm: pgtable: introduce pte_offset_map_{ro|rw}_nolock() To: Qi Zheng , hughd@google.com, willy@infradead.org, muchun.song@linux.dev, vbabka@kernel.org, akpm@linux-foundation.org, rppt@kernel.org, vishal.moola@gmail.com, peterx@redhat.com, ryan.roberts@arm.com, christophe.leroy2@cs-soprasteria.com Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org References: <1a4fea06f8cada72553a8d8992a92e9c09f2c9d4.1727148662.git.zhengqi.arch@bytedance.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: <1a4fea06f8cada72553a8d8992a92e9c09f2c9d4.1727148662.git.zhengqi.arch@bytedance.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-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: 11AFA18000D X-Stat-Signature: a83s84ybosi1egorxek7qb8d69meonnt X-HE-Tag: 1727182707-160439 X-HE-Meta: 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 hbHtmV78 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 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 24.09.24 08:09, Qi Zheng wrote: > Currently, the usage of pte_offset_map_nolock() can be divided into the > following two cases: > > 1) After acquiring PTL, only read-only operations are performed on the PTE > page. In this case, the RCU lock in pte_offset_map_nolock() will ensure > that the PTE page will not be freed, and there is no need to worry > about whether the pmd entry is modified. > > 2) After acquiring PTL, the pte or pmd entries may be modified. At this > time, we need to ensure that the pmd entry has not been modified > concurrently. > > To more clearing distinguish between these two cases, this commit > introduces two new helper functions to replace pte_offset_map_nolock(). > For 1), just rename it to pte_offset_map_ro_nolock(). For 2), in addition > to changing the name to pte_offset_map_rw_nolock(), it also outputs the > pmdval when successful. It is applicable for may-write cases where any > modification operations to the page table may happen after the > corresponding spinlock is held afterwards. But the users should make sure > the page table is stable like checking pte_same() or checking pmd_same() > by using the output pmdval before performing the write operations. > > Note: "RO" / "RW" expresses the intended semantics, not that the *kmap* > will be read-only/read-write protected. > > Subsequent commits will convert pte_offset_map_nolock() into the above > two functions one by one, and finally completely delete it. > > Signed-off-by: Qi Zheng > --- Acked-by: David Hildenbrand -- Cheers, David / dhildenb