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[2003:cb:c709:600:4306:6a2b:57d5:2da1]) by smtp.gmail.com with ESMTPSA id y6-20020a05600c364600b003f420667807sm6207453wmq.11.2023.05.25.09.45.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 25 May 2023 09:45:08 -0700 (PDT) Message-ID: Date: Thu, 25 May 2023 18:45:07 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0 Subject: Re: Extending page pinning into fs/direct-io.c To: Linus Torvalds , David Howells Cc: Christoph Hellwig , Jens Axboe , Al Viro , Matthew Wilcox , Jan Kara , Jeff Layton , Jason Gunthorpe , Logan Gunthorpe , Hillf Danton , Christian Brauner , linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20230522205744.2825689-1-dhowells@redhat.com> <3068545.1684872971@warthog.procyon.org.uk> <3215177.1684918030@warthog.procyon.org.uk> From: David Hildenbrand 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: 8bit X-Stat-Signature: g11uhu85rp4n4up4pqk1gxqh4dnhciqm X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 3E592140020 X-Rspam-User: X-HE-Tag: 1685033112-873430 X-HE-Meta: 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 hglzyceV MWjao27V4wmpirg5p12NPJmvLfLQTWn3qrXhAXqrthoj7dz2sSCxSzh5P6k+s71WVCQBRQyTIpvvKigxBh5xs+jGQ/4MSy+qnpfty61qIYiVT4TLX7E3fef1kmqv90T2XQ90yjRhtuNsN799FGxTjxBl5d0S7HaFZICFNsRweuF7YMz9Om0e/dfGoEjr2uFLbjS8FRQrf/2P5LxvZKlnisskxDKzSw4u5nbDQV8fknVVmVNrJdkAdwBjR7rR1grJrZevHJkLF4DuHq11wwmvn/qZcOXCXEfjUv9vAC7kZjV5WnQL7IEIueN+2QUoZnmZLVxbqa/1pLtXpngmPIfH7cjhFmZ2EoW18kI77hKDoFAyCXyrrhSOjlSIKuXPlDXOTGHjUVUwcuD96Ug22OWLVmRUwJDOyT4gfheLd 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 25.05.23 18:31, Linus Torvalds wrote: > On Wed, May 24, 2023 at 1:47 AM David Howells wrote: >> >> True - but I was thinking of just treating the zero_page specially and never >> hold a pin or a ref on it. It can be checked by address, e.g.: >> >> static inline void bio_release_page(struct bio *bio, struct page *page) >> { >> if (page == ZERO_PAGE(0)) >> return; > > That won't actually work. > > We do have cases that try to use the page coloring that we support. > > Admittedly it seems to be only rmda that does it directly with > something like this: > > vmf->page = ZERO_PAGE(vmf->address); > > but you can get arbitrary zero pages by pinning or GUPing them from > user space mappings. > > Now, the only architectures that *use* multiple zero pages are - I > think - MIPS (including Loongarch) and s390. > > So it's rare, but it does happen. I think the correct way to test for a zero page is is_zero_pfn(page_to_pfn(page). Using my_zero_pfn(vmf->address) in do_anonymous_page() these can easily end up in any process. -- Thanks, David / dhildenb