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David Howells c8070b7875 mm: Don't pin ZERO_PAGE in pin_user_pages()
Make pin_user_pages*() leave a ZERO_PAGE unpinned if it extracts a pointer
to it from the page tables and make unpin_user_page*() correspondingly
ignore a ZERO_PAGE when unpinning.  We don't want to risk overrunning a
zero page's refcount as we're only allowed ~2 million pins on it -
something that userspace can conceivably trigger.

Add a pair of functions to test whether a page or a folio is a ZERO_PAGE.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Christoph Hellwig <hch@infradead.org>
cc: David Hildenbrand <david@redhat.com>
cc: Lorenzo Stoakes <lstoakes@gmail.com>
cc: Andrew Morton <akpm@linux-foundation.org>
cc: Jens Axboe <axboe@kernel.dk>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: Matthew Wilcox <willy@infradead.org>
cc: Jan Kara <jack@suse.cz>
cc: Jeff Layton <jlayton@kernel.org>
cc: Jason Gunthorpe <jgg@nvidia.com>
cc: Logan Gunthorpe <logang@deltatee.com>
cc: Hillf Danton <hdanton@sina.com>
cc: Christian Brauner <brauner@kernel.org>
cc: Linus Torvalds <torvalds@linux-foundation.org>
cc: linux-fsdevel@vger.kernel.org
cc: linux-block@vger.kernel.org
cc: linux-kernel@vger.kernel.org
cc: linux-mm@kvack.org
Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: David Hildenbrand <david@redhat.com>
Link: https://lore.kernel.org/r/20230526214142.958751-2-dhowells@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2023-05-31 09:48:15 -06:00
arch
block block: constify the whole_disk device_attribute 2023-05-30 11:12:43 -06:00
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Documentation mm: Don't pin ZERO_PAGE in pin_user_pages() 2023-05-31 09:48:15 -06:00
drivers Merge branch 'for-6.5/splice' into for-6.5/block 2023-05-24 08:42:22 -06:00
fs block: Replace BIO_NO_PAGE_REF with BIO_PAGE_REFFED with inverted logic 2023-05-24 08:42:44 -06:00
include mm: Don't pin ZERO_PAGE in pin_user_pages() 2023-05-31 09:48:15 -06:00
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lib iov_iter: Kill ITER_PIPE 2023-05-24 08:42:17 -06:00
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mm mm: Don't pin ZERO_PAGE in pin_user_pages() 2023-05-31 09:48:15 -06:00
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Linux kernel
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