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[2003:cb:c72f:c700:a76f:473d:d5cf:25a8]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-37d1691a47esm7476182f8f.28.2024.10.08.01.21.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 08 Oct 2024 01:21:11 -0700 (PDT) Message-ID: <7201c25f-0b6e-4a8b-b6a1-b09c6730fb32@redhat.com> Date: Tue, 8 Oct 2024 10:21:10 +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 Cc: Jann Horn , 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> <75fac79a-0ff2-4ba0-bdd7-954efe2d9f41@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-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Stat-Signature: ozbenig39i3hhh5yhkon9gtxq8awb4gy X-Rspamd-Queue-Id: 489FB140003 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1728375675-888121 X-HE-Meta: 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 TCXnpbqx 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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 08.10.24 09:58, Qi Zheng wrote: > > > On 2024/10/8 15:52, David Hildenbrand wrote: >> 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? > > Ah, make sense. > > Acked-by: Qi Zheng Thanks a lot for your review! -- Cheers, David / dhildenb