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[2003:cb:c706:4e00:31ad:5274:e21c:b59]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4281c3cc71fsm88211015e9.39.2024.07.30.08.49.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 30 Jul 2024 08:49:11 -0700 (PDT) Message-ID: <82e77547-5116-4ef2-a232-f5ab1fca7e02@redhat.com> Date: Tue, 30 Jul 2024 17:49:10 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 1/2] mm: let pte_lockptr() consume a pte_t pointer From: David Hildenbrand To: Marek Szyprowski , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Andrew Morton , Muchun Song , Peter Xu , Oscar Salvador References: <20240725183955.2268884-1-david@redhat.com> <20240725183955.2268884-2-david@redhat.com> <97d87df8-6076-4df0-90a9-a8f5ddea42e9@samsung.com> 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: 7bit X-Rspam-User: X-Stat-Signature: bd7ffn1tmd8jtu88juagzcsz4sm7tjm1 X-Rspamd-Queue-Id: DFA9340020 X-Rspamd-Server: rspam11 X-HE-Tag: 1722354559-654098 X-HE-Meta: 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 eygICn0x 1u05Pk2sVxF72k+h9ThzlYC/VGURMYqOJNWChPSqTLCtzq0dozWli7KLF79nwYFf88MoqoFyPhIdJDXOlt/q8A3jFCFUHHjdp/GIcE23sJ00D/frX6tZqXup87+XHWqfnsFytu4OtlYV83fNguEgzSSplwVF3i1eJQqIV26b9eHnITvoxe10i0Lb2asG6DuDUuFjTh1tJHQytHrUL/oGFgUWZslS/jY/v1lVII7LsfGysvNpi76DrAHExdY02yVgrb4h26i93SmzMq4B8bZYPwekq0xXxk5ZBhnLf0cnPUmw5JLBHPlsB81AN2u5hDyoOY1nW1hvivEs9zuck6JaCwAjH2MpHTdoRJMfZVGTmUBTcehwpgt0eSFaN0vVw+WcBVeNiovRufkxm+2olfb+Ck8FrF1DhlVM++8xsxxDEoy2v0D9CGdgPKTaBKHPn6jVZGrtg 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 30.07.24 17:45, David Hildenbrand wrote: > On 30.07.24 17:30, Marek Szyprowski wrote: >> On 25.07.2024 20:39, David Hildenbrand wrote: >>> pte_lockptr() is the only *_lockptr() function that doesn't consume >>> what would be expected: it consumes a pmd_t pointer instead of a pte_t >>> pointer. >>> >>> Let's change that. The two callers in pgtable-generic.c are easily >>> adjusted. Adjust khugepaged.c:retract_page_tables() to simply do a >>> pte_offset_map_nolock() to obtain the lock, even though we won't actually >>> be traversing the page table. >>> >>> This makes the code more similar to the other variants and avoids other >>> hacks to make the new pte_lockptr() version happy. pte_lockptr() users >>> reside now only in pgtable-generic.c. >>> >>> Maybe, using pte_offset_map_nolock() is the right thing to do because >>> the PTE table could have been removed in the meantime? At least it sounds >>> more future proof if we ever have other means of page table reclaim. >>> >>> It's not quite clear if holding the PTE table lock is really required: >>> what if someone else obtains the lock just after we unlock it? But we'll >>> leave that as is for now, maybe there are good reasons. >>> >>> This is a preparation for adapting hugetlb page table locking logic to >>> take the same locks as core-mm page table walkers would. >>> >>> Signed-off-by: David Hildenbrand >> >> This patch landed in today's linux-next as commit e98970a1d2d4 ("mm: let >> pte_lockptr() consume a pte_t pointer"). Unfortunately it causes the >> following issue on most of my ARM 32bit based test boards: >> > > That is ... rather surprising. > > The issue below seems to point at __pte_offset_map_lock(), where we > essentially convert from > > ptlock_ptr(page_ptdesc(pmd_page(*pmd))); > > to > > ptlock_ptr(virt_to_ptdesc(pte)); I'm wondering, is highmem involved here such that the PTE would be kmap'ed and virt_to_page() would not do what we would expect it to do? -- Cheers, David / dhildenb