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(p200300cbc739bb00201f378f5564caeb.dip0.t-ipconnect.de. [2003:cb:c739:bb00:201f:378f:5564:caeb]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-368787cec6bsm13754705f8f.71.2024.07.24.01.53.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 24 Jul 2024 01:53:54 -0700 (PDT) Message-ID: <2190c4dc-ae84-4781-8e86-4b2ca99f2237@redhat.com> Date: Wed, 24 Jul 2024 10:53:52 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/x86/pat: Only untrack the pfn range if unmap region To: Jason Gunthorpe Cc: Peter Xu , Yan Zhao , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , Andrew Morton , Alex Williamson , Al Viro , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , "Kirill A . Shutemov" , "x86@kernel.org" , "Tian, Kevin" , Pei Li , David Wang <00107082@163.com>, Bert Karwatzki , Sergey Senozhatsky References: <1a0884cb-39ed-455e-a505-7c1b2a0e5225@redhat.com> <56c982c4-9863-4134-b088-8dfb4b94c531@redhat.com> <20240723214412.GQ3371438@nvidia.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: <20240723214412.GQ3371438@nvidia.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: rspam11 X-Rspamd-Queue-Id: 3289018000C X-Stat-Signature: jpm473sbgksezer5ghgw5ij4xbetidn5 X-Rspam-User: X-HE-Tag: 1721811240-925347 X-HE-Meta: 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 5CIusesc LuieTzE4KRL3i/Tt0d/ag3BrKOFmvYIezGEUvrRAPb1+4fJlASx7g3GPDPjSKOXz1HoymtIoE1t4inPI4C04DbBTF3jy5UFiF9A6V7Iw3ztRHQZl+aGrYjVi7h0K5gPQXz4Tb+sABjI+o+clvZNJPhHNrjslzGZKXEarRERaSF0Lxcz2yPQfXe1U89FWdlGaYLSmIuq9LWMa0UhK4P0c3vV34InDsil1DZ3E4Md06mAQp8TEYRo8odoZqEja2KNbORON5ZawamBZxqaegl60veawlOcfe8ykXEaYqCSR1A0gvJHmkW4wyVIcKOlSXZEal99+VZVdUKXbD1WBdfuvfXdwzkGnOXYiI3Hhm6yagxsMofYefscfMENLlAIe4OoyDDRi2lNf4Nf/ZMwa6su36G2N79PAbx7mVNXscDtE+Otk22kXydLNKNLK05LYpeYLO8zzKMsoLanmaZENHsyAwtgu22sUQFVQDUC/8FVQNrDUldWc= 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 23.07.24 23:44, Jason Gunthorpe wrote: > On Tue, Jul 23, 2024 at 11:36:51PM +0200, David Hildenbrand wrote: >> I wonder if we could just let relevant users do the PAT handling manually: >> I'm also not sure how many remap_pfn_range users end up triggering VM_PAT >> code although they don't really have to (just because they happen to cover a >> full VMA)? >> >> One nasty thing is fork(), I was wondering if relevant users really rely on >> that or if we could force these VMAs to simply not get copied during fork. >> During fork() we have to "duplicate" the reservation ... > > I admit I barely understand what x86 uses this PAT stuff for - > allowing WC mappings is part of it? I'm confused by all of that, but I think yes :) > > If yes, then RDMA would expect WC PFN MAP VMAs to copy their WCness > during fork.. Okay, that answers that question: we have to support fork(). During fork() we call vm_ops->open when cloning the VMA. So the backend can realize when all users (VMAs, whatsoever) are gone to undo any registration. Maybe that's a path forward. But still no clue on details ... one important step might be figuring out who exactly really relies on that VM_PAT handling. -- Cheers, David / dhildenb