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[2003:cb:c736:1000:9e30:2a8a:cd3d:419c]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-43bc38986cbsm68968655e9.35.2025.03.04.07.51.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 04 Mar 2025 07:51:18 -0800 (PST) Message-ID: <9d04c204-cb9a-4109-977b-3d39b992c521@redhat.com> Date: Tue, 4 Mar 2025 16:51:16 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 4/5] KVM: guest_memfd: Enforce NUMA mempolicy using shared policy To: Sean Christopherson , Ackerley Tng Cc: Vlastimil Babka , shivankg@amd.com, akpm@linux-foundation.org, willy@infradead.org, pbonzini@redhat.com, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-coco@lists.linux.dev, chao.gao@intel.com, bharata@amd.com, nikunj@amd.com, michael.day@amd.com, Neeraj.Upadhyay@amd.com, thomas.lendacky@amd.com, michael.roth@amd.com, tabba@google.com References: 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: EZlBuAOOWUFJQuTCFJtXB9pTW2tuSoViZK7xKieLsSg_1741103480 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: p7fqs7esuaxzu7fuuymatt66y9jwswdw X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: CA09940007 X-Rspam-User: X-HE-Tag: 1741103494-793743 X-HE-Meta: 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 z7PIhVSl bBn2e2FaVU1IX72LbbYEml30NRSLr528aQMtqmu5gfVLlUr8reDDcnSUwptwc7/eBT4M64DFnXo2OLFbGgVAn+xZyMgDSxjF19mV4CdjgzI6kRPHf1K3Y8kYzJ9dNoHcJLqWue9PX7KkuFujiXZV/RYkI+0LPoF10CiNmG57TWWeh8J87gpQzImaAINd8EuH52KrgUKjyaq6RAUhXBlYUl3lzb2faWHaRbj/VQvE5BRWY+ESWMJdsrPK0pHO2yPpTde0CLowH7fAeDSNXFU4PfJEe5KobV6zCz+7MyeApA+sD3YKGkiSyd0KwDI1kI1u8LRF1PRW0OxWPI+czFhAaxq6d+8C2PQKjKkiZlOLtOSA8cVTGaCI5brBz3LiEYN6zL5+DFSdQgFV9MiLACNzvR4G4+lXeBsEmP+TZfVlxculY/7g8vGBwWN0i6TVQwz+qI5Ls X-Bogosity: Ham, tests=bogofilter, spamicity=0.000389, 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 04.03.25 16:30, Sean Christopherson wrote: > On Tue, Mar 04, 2025, Ackerley Tng wrote: >> Vlastimil Babka writes: >>>> struct shared_policy should be stored on the inode rather than the file, >>>> since the memory policy is a property of the memory (struct inode), >>>> rather than a property of how the memory is used for a given VM (struct >>>> file). >>> >>> That makes sense. AFAICS shmem also uses inodes to store policy. >>> >>>> When the shared_policy is stored on the inode, intra-host migration [1] >>>> will work correctly, since the while the inode will be transferred from >>>> one VM (struct kvm) to another, the file (a VM's view/bindings of the >>>> memory) will be recreated for the new VM. >>>> >>>> I'm thinking of having a patch like this [2] to introduce inodes. >>> >>> shmem has it easier by already having inodes >>> >>>> With this, we shouldn't need to pass file pointers instead of inode >>>> pointers. >>> >>> Any downsides, besides more work needed? Or is it feasible to do it using >>> files now and convert to inodes later? >>> >>> Feels like something that must have been discussed already, but I don't >>> recall specifics. >> >> Here's where Sean described file vs inode: "The inode is effectively the >> raw underlying physical storage, while the file is the VM's view of that >> storage." [1]. >> >> I guess you're right that for now there is little distinction between >> file and inode and using file should be feasible, but I feel that this >> dilutes the original intent. > > Hmm, and using the file would be actively problematic at some point. One could > argue that NUMA policy is property of the VM accessing the memory, i.e. that two > VMs mapping the same guest_memfd could want different policies. But in practice, > that would allow for conflicting requirements, e.g. different policies in each > VM for the same chunk of memory, and would likely lead to surprising behavior due > to having to manually do mbind() for every VM/file view. I think that's the same behavior with shmem? I mean, if you have two people asking for different things for the same MAP_SHARE file range, surprises are unavoidable. Or am I missing something? -- Cheers, David / dhildenb