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[86.156.84.164]) by smtp.gmail.com with ESMTPSA id o5-20020a5d58c5000000b002f47ae62fe0sm10547708wrf.115.2023.04.17.06.19.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Apr 2023 06:19:17 -0700 (PDT) Date: Mon, 17 Apr 2023 14:19:16 +0100 From: Lorenzo Stoakes To: Jason Gunthorpe Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Matthew Wilcox , David Hildenbrand , Jens Axboe , Pavel Begunkov , io-uring@vger.kernel.org Subject: Re: [PATCH 5/7] io_uring: rsrc: use FOLL_SAME_FILE on pin_user_pages() Message-ID: References: <17357dec04b32593b71e4fdf3c30a346020acf98.1681508038.git.lstoakes@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Queue-Id: 57E92C0017 X-Rspamd-Server: rspam01 X-Stat-Signature: mob5jogabjj7bbif7p843hf68c35x5oh X-HE-Tag: 1681737560-849045 X-HE-Meta: U2FsdGVkX199rnhJ8aqDVnE9AD5uTwbMuThKUCc83+WdInB0fC43J3j2Nd6/ab9ctKeSd5A9I4ZCSuV1gkSc8Fc329E4Q6zTvAsnHhashvDNsWk5VBvdYhFjpdA4CxaQBkYbAWRyzryotfhwIg2aC51PsbXiUIKmf5N2md6AF/pqN3w/9PPiOzpCMjSoPOIv/Rh6kWDdeHkRodTXzc1bP8LAcx6/SSMGNp17vSUZI4lLVv2UJ0es+lD4+sUlrZg79Nta89MDGbZbRBlKxKG358Vpd5hDji1TnIXMzcWk7J7P/UgK9pXnp8SQ0SoK8kFKA9hCyvB0dhLwWD56LC5EOAEklB2vVGv1fTVIsO/QxTCRzAlERkrH9bkXMBOiQG40oxOO7ZVKGbjuUZb1FnWHm52/V+LaR3/yTfV3nyQWWDhZYshvvWov8AZyg14hnUkJp554yFUlFQHFFeQ7p/NOAPNte6RC+G398qJwBridL85DAhW1jL9nEdnZHIPz9zG0S3xSGc+WcMQMCklZDXwDijNO4O7LF9hhznSHS1UF1cioWu9/Jzk6Ujy+aUkK2/0j3qk9x0fY4SWuwm87VINGc8OvAeIsIKIJeuLLtuUzeyf8JfqVrktbpTvfxJeQtFLKCFq3qnhAxMxlyIGXQh1zoQgGerr8kqWnf9Q1vTJgCVkkwY2UL2Gp6oq3ae5v7SF3kzo/0YgnNrH2tmv7a7iA1yP+2jrYWwk22qfvBhwW5cc3PAmx5oO76vfRVH0wM54FChOfyqaFgS25pjoZnHu/QPQgKK+ReY45JX68+A9mXBJvwxZLOD28xroOMV2sV6t9fhm7XQMal0E/Xd68O5QC93kWIgFqUoX8yoq77Y4bwPoPaOdxsXuuq0VRFiV3YAWhz/cl1iSiPpTCf/Vpsl1jsCa/b26p/rzQ296BUJ4c8WaD2ekFdUiG/QEC7M4paNTZ1x3YGOx54byMN2rF4J2 DaY+TbGE 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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: On Mon, Apr 17, 2023 at 09:56:34AM -0300, Jason Gunthorpe wrote: > On Sat, Apr 15, 2023 at 12:27:45AM +0100, Lorenzo Stoakes wrote: > > Commit edd478269640 ("io_uring/rsrc: disallow multi-source reg buffers") > > prevents io_pin_pages() from pinning pages spanning multiple VMAs with > > permitted characteristics (anon/huge), requiring that all VMAs share the > > same vm_file. > > That commmit doesn't really explain why io_uring is doing such a weird > thing. > > What exactly is the problem with mixing struct pages from different > files and why of all the GUP users does only io_uring need to care > about this? > > If there is no justification then lets revert that commit instead. > > > /* don't support file backed memory */ > > - for (i = 0; i < nr_pages; i++) { > > - if (vmas[i]->vm_file != file) { > > - ret = -EINVAL; > > - break; > > - } > > - if (!file) > > - continue; > > - if (!vma_is_shmem(vmas[i]) && !is_file_hugepages(file)) { > > - ret = -EOPNOTSUPP; > > - break; > > - } > > - } > > + file = vma->vm_file; > > + if (file && !vma_is_shmem(vma) && !is_file_hugepages(file)) > > + ret = -EOPNOTSUPP; > > + > > Also, why is it doing this? > > All GUP users don't work entirely right for any fops implementation > that assumes write protect is unconditionally possible. eg most > filesystems. > > We've been ignoring blocking it because it is an ABI break and it does > sort of work in some cases. > I will leave this to Jens and Pavel to revert on! > I'd rather see something like FOLL_ALLOW_BROKEN_FILE_MAPPINGS than > io_uring open coding this kind of stuff. > How would the semantics of this work? What is broken? It is a little frustrating that we have FOLL_ANON but hugetlb as an outlying case, adding FOLL_ANON_OR_HUGETLB was another consideration... > Jason