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| author | David Howells <dhowells@redhat.com> | 2023-05-26 22:41:40 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2025-03-07 16:56:47 +0100 |
| commit | 476c1dfefab8b98ae9c3e3ad283c2ac10d30c774 (patch) | |
| tree | 10d884db93dcec0855a6c35852628070b2d82ea2 /Documentation | |
| parent | cffd76d4e9ab575e8f5396f88922008cf973e1c4 (diff) | |
| download | linux-476c1dfefab8b98ae9c3e3ad283c2ac10d30c774.tar.gz linux-476c1dfefab8b98ae9c3e3ad283c2ac10d30c774.tar.bz2 linux-476c1dfefab8b98ae9c3e3ad283c2ac10d30c774.zip | |
mm: Don't pin ZERO_PAGE in pin_user_pages()
[ Upstream commit c8070b78751955e59b42457b974bea4a4fe00187 ]
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>
Stable-dep-of: bddf10d26e6e ("uprobes: Reject the shared zeropage in uprobe_write_opcode()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/core-api/pin_user_pages.rst | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/Documentation/core-api/pin_user_pages.rst b/Documentation/core-api/pin_user_pages.rst index b18416f4500f..7995ce2b9676 100644 --- a/Documentation/core-api/pin_user_pages.rst +++ b/Documentation/core-api/pin_user_pages.rst @@ -113,6 +113,12 @@ pages: This also leads to limitations: there are only 31-10==21 bits available for a counter that increments 10 bits at a time. +* Because of that limitation, special handling is applied to the zero pages + when using FOLL_PIN. We only pretend to pin a zero page - we don't alter its + refcount or pincount at all (it is permanent, so there's no need). The + unpinning functions also don't do anything to a zero page. This is + transparent to the caller. + * Callers must specifically request "dma-pinned tracking of pages". In other words, just calling get_user_pages() will not suffice; a new set of functions, pin_user_page() and related, must be used. |