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[2003:cb:c72f:c700:a76f:473d:d5cf:25a8]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43017465f3bsm15971755e9.0.2024.10.08.00.52.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 08 Oct 2024 00:52:38 -0700 (PDT) Message-ID: <75fac79a-0ff2-4ba0-bdd7-954efe2d9f41@redhat.com> Date: Tue, 8 Oct 2024 09:52:37 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/mremap: Fix move_normal_pmd/retract_page_tables race To: Qi Zheng , Jann Horn Cc: akpm@linux-foundation.org, linux-mm@kvack.org, willy@infradead.org, hughd@google.com, lorenzo.stoakes@oracle.com, joel@joelfernandes.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20241007-move_normal_pmd-vs-collapse-fix-2-v1-1-5ead9631f2ea@google.com> <1c114925-9206-42b1-b24b-bb123853a359@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: <1c114925-9206-42b1-b24b-bb123853a359@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-Rspam-User: X-Stat-Signature: set8qzfweaxgpfjqzomx6suadi1syjqf X-Rspamd-Queue-Id: 152D040017 X-Rspamd-Server: rspam02 X-HE-Tag: 1728373962-190312 X-HE-Meta: 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 imVTYzCi 2R5kIRnsmDZBws5Tyezax6q1GpBw4+RfKPnDHD8cKmECjxW+8YpCsTtNkJWyU50A5Q1PG1Hs+VB6yF+JfV2SEtjP8lKVXt/wMkVo6SxbOr8JEQbMYOW5oxHOBrA5YXSJLVoTsWdUNxaYTcoMcgiZkCxD4eblkfe8na/TFnCMwYqTWb5lbJRJ8ErRxB1oAr+M6Rd9HMBDU/kDV5jptKCzsIDSzibOeCI2nMo4CQCtPGcSTvXdAWcIBbqN64IWTQbuw5hURcVK6jCXS/kDxALimylMt+mExb6PBZ6QBI5PFoJtunD+LURMkjtB5N30OGOcdBQgx6mZrdfbzre5Vc6Q8KXg0t+CFsuzPKK+ajjyZNFq1N91GTYnjYGKwWq7ygxIZE3ucemU2f1icS77Dtrco8dG9zA8EqYhcMhWXIzdDjLYuQqt59XRRy+qyKlnzKjbMXQQh 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 08.10.24 05:53, Qi Zheng wrote: > Hi Jann, > > On 2024/10/8 05:42, Jann Horn wrote: > > [...] > >> >> diff --git a/mm/mremap.c b/mm/mremap.c >> index 24712f8dbb6b..dda09e957a5d 100644 >> --- a/mm/mremap.c >> +++ b/mm/mremap.c >> @@ -238,6 +238,7 @@ static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr, >> { >> spinlock_t *old_ptl, *new_ptl; >> struct mm_struct *mm = vma->vm_mm; >> + bool res = false; >> pmd_t pmd; >> >> if (!arch_supports_page_table_move()) >> @@ -277,19 +278,25 @@ static bool move_normal_pmd(struct vm_area_struct *vma, unsigned long old_addr, >> if (new_ptl != old_ptl) >> spin_lock_nested(new_ptl, SINGLE_DEPTH_NESTING); >> >> - /* Clear the pmd */ >> pmd = *old_pmd; >> + >> + /* Racing with collapse? */ >> + if (unlikely(!pmd_present(pmd) || pmd_leaf(pmd))) > > Since we already hold the exclusive mmap lock, after a racing > with collapse occurs, the pmd entry cannot be refilled with > new content by page fault. So maybe we only need to recheck > pmd_none(pmd) here? My thinking was that it is cheap and more future proof to check that we really still have a page table here. For example, what if collapse code is ever changed to replace the page table by the collapsed PMD? So unless there is a good reason not to have this check here, I would keep it like that. Thanks! -- Cheers, David / dhildenb