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[2003:cb:c711:c600:c1d6:7158:f946:f083]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-a89891dacb2sm91262266b.183.2024.08.29.08.36.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 29 Aug 2024 08:36:08 -0700 (PDT) Message-ID: <4101a941-6286-4128-a16c-29c7cffcbe8c@redhat.com> Date: Thu, 29 Aug 2024 17:36:07 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 08/14] mm: copy_pte_range() use pte_offset_map_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: <71100c3867c4cf6f5f429ce9f2db8432066d0e99.1724310149.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: <71100c3867c4cf6f5f429ce9f2db8432066d0e99.1724310149.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: rspam06 X-Rspamd-Queue-Id: 1423140025 X-Stat-Signature: rqrgsoiubc3qsz9tyhqmkaje5fj4h9n4 X-Rspam-User: X-HE-Tag: 1724945774-196585 X-HE-Meta: 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 Du9MeUyk 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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 22.08.24 09:13, Qi Zheng wrote: > In copy_pte_range(), we may modify the src_pte entry after holding the > src_ptl, so convert it to using pte_offset_map_rw_nolock(). But since we > already hold the write lock of mmap_lock, there is no need to get pmdval > to do pmd_same() check, just pass a dummy variable to it. > > Signed-off-by: Qi Zheng > --- > mm/memory.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 7b6071a0e21e2..30d98025b2a40 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -1083,6 +1083,7 @@ copy_pte_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, > struct mm_struct *src_mm = src_vma->vm_mm; > pte_t *orig_src_pte, *orig_dst_pte; > pte_t *src_pte, *dst_pte; > + pmd_t dummy_pmdval; > pte_t ptent; > spinlock_t *src_ptl, *dst_ptl; > int progress, max_nr, ret = 0; > @@ -1108,7 +1109,15 @@ copy_pte_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma, > ret = -ENOMEM; > goto out; > } > - src_pte = pte_offset_map_nolock(src_mm, src_pmd, addr, &src_ptl); > + > + /* > + * Use the maywrite version to indicate that dst_pte will be modified, > + * but since we already hold the write lock of mmap_lock, there is no > + * need to get pmdval to do pmd_same() check, just pass a dummy variable > + * to it. As we hold the mmap lock write lock, I assume it will prevent any page table removal, because they need *at least* the mmap lock in read mode, right? We should probably document the rules for removing a page table -- which locks must be held in which mode (if not already done). -- Cheers, David / dhildenb