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[2003:cb:c734:9600:af27:4326:a216:2bfb]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43bbf2edf84sm52002545e9.40.2025.03.03.08.36.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 03 Mar 2025 08:36:26 -0800 (PST) Message-ID: Date: Mon, 3 Mar 2025 17:36:25 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 0/2] SKSM: Synchronous Kernel Samepage Merging To: Peter Xu , Mathieu Desnoyers Cc: Linus Torvalds , Andrew Morton , linux-kernel@vger.kernel.org, Matthew Wilcox , Olivier Dion , linux-mm@kvack.org References: <20250228023043.83726-1-mathieu.desnoyers@efficios.com> <8524caa9-e1f6-4411-b86b-d9457ddb8007@efficios.com> <60f148db-7586-4154-a909-d433bad39794@efficios.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-MFC-PROC-ID: IHIh1NT4kBlsRIHs7gcMbegx6J1fxoNvS1ySO2K1jwE_1741019788 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-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: ACB152000B X-Stat-Signature: y6oaycar4fcg6yudrd9y56ojqzmrfkks X-HE-Tag: 1741019806-627957 X-HE-Meta: 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 eLAwEOvG aItkMk47wlsggHoPk5pg7WImorps3tB2bC97GsyWzJvs7ROVw75OF9oPZQFEEN53Hci8jv1GAu10D0BAOsnFkAKS4M7D7gAbkRB+XCEA4CUJoX0tFcjSthGf2CxQUyJBoIRjnxvVRn7UPELXLF6DfJkRJ3T4nxpconL7RTeuPNhTomoROPKYEDAavaMN9Xv5tIh3TYGur+SJVf8xlqVvwXxusqiUPULqRqeZ3mqjIDzh7KI9TSjvcXbxMwpDY3l5swkQDkBoBmJp45IB4pwRzm3EcQ017sLOt6GrivWPkaQeMQ8hXr74XN4jMcV94HsG99dbNSqxoB5gk8OJZOKVCNE/XwFuTbvY6Zu2BcUUyDMFnmNnJz65yFkFn5DnYf32P3yfFmHZ7/uHrlNvUMdFdjTmvv4nyh/l5sUCh 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 03.03.25 16:01, Peter Xu wrote: > On Sat, Mar 01, 2025 at 10:44:22AM -0500, Mathieu Desnoyers wrote: >>>> Also, I notice that do_wp_page() only calls handle_userfault >>>> VM_UFFD_WP when vm_fault flags does not have FAULT_FLAG_UNSHARE >>>> set. >>> >>> AFAICT that's expected, unshare should only be set on reads, never writes. >>> So uffd-wp shouldn't trap any of those. >> >> I'm confused by your comment. I thought unshare only applies to >> *write* faults. What am I missing ? > > The major path so far to set unshare is here in GUP (ignoring two corner > cases used in either s390 and ksm): "unshare" fault, in contrast to a write fault, will not turn the PTE writable. That's why it does not trigger userfaultfd-wp: there is no write access, write-protection is left unchanged. -- Cheers, David / dhildenb