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John Hubbard 3faa52c03f mm/gup: track FOLL_PIN pages
Add tracking of pages that were pinned via FOLL_PIN.  This tracking is
implemented via overloading of page->_refcount: pins are added by adding
GUP_PIN_COUNTING_BIAS (1024) to the refcount.  This provides a fuzzy
indication of pinning, and it can have false positives (and that's OK).
Please see the pre-existing Documentation/core-api/pin_user_pages.rst for
details.

As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN
(typically via pin_user_pages*()) are required to ultimately free such
pages via unpin_user_page().

Please also note the limitation, discussed in pin_user_pages.rst under the
"TODO: for 1GB and larger huge pages" section.  (That limitation will be
removed in a following patch.)

The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be
thought of as "FOLL_GET for DIO and/or RDMA use".

Pages that have been pinned via FOLL_PIN are identifiable via a new
function call:

   bool page_maybe_dma_pinned(struct page *page);

What to do in response to encountering such a page, is left to later
patchsets. There is discussion about this in [1], [2], [3], and [4].

This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask().

[1] Some slow progress on get_user_pages() (Apr 2, 2019):
    https://lwn.net/Articles/784574/
[2] DMA and get_user_pages() (LPC: Dec 12, 2018):
    https://lwn.net/Articles/774411/
[3] The trouble with get_user_pages() (Apr 30, 2018):
    https://lwn.net/Articles/753027/
[4] LWN kernel index: get_user_pages():
    https://lwn.net/Kernel/Index/#Memory_management-get_user_pages

[jhubbard@nvidia.com: add kerneldoc]
  Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com
[imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page will not be enough]
  Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm.com
[akpm@linux-foundation.org: fix put_compound_head defined but not used]
Suggested-by: Jan Kara <jack@suse.cz>
Suggested-by: Jérôme Glisse <jglisse@redhat.com>
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-04-02 09:35:27 -07:00
Documentation mm/gup: track FOLL_PIN pages 2020-04-02 09:35:27 -07:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch asm-generic: make more kernel-space headers mandatory 2020-04-02 09:35:25 -07:00
block Merge branch 'efi-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2020-03-30 16:13:08 -07:00
certs certs: Add wrapper function to check blacklisted binary hash 2019-11-12 12:25:50 +11:00
crypto Merge branch 'next-integrity' of git://git.kernel.org/pub/scm/linux/kernel/git/zohar/linux-integrity 2020-02-20 15:15:16 -08:00
drivers Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next 2020-03-31 17:29:33 -07:00
fs fs_parse: remove pr_notice() about each validation 2020-04-02 09:35:26 -07:00
include mm/gup: track FOLL_PIN pages 2020-04-02 09:35:27 -07:00
init Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next 2020-03-31 17:29:33 -07:00
ipc Revert "ipc,sem: remove uneeded sem_undo_list lock usage in exit_sem()" 2020-02-21 11:22:15 -08:00
kernel Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next 2020-03-31 17:29:33 -07:00
lib Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next 2020-03-31 17:29:33 -07:00
mm mm/gup: track FOLL_PIN pages 2020-04-02 09:35:27 -07:00
net Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next 2020-03-31 17:29:33 -07:00
samples Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next 2020-03-31 17:29:33 -07:00
scripts scripts/spelling.txt: add more spellings to spelling.txt 2020-04-02 09:35:25 -07:00
security Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next 2020-03-31 17:29:33 -07:00
sound Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next 2020-03-31 17:29:33 -07:00
tools tools/accounting/getdelays.c: fix netlink attribute length 2020-04-02 09:35:25 -07:00
usr initramfs: restore default compression behavior 2020-03-17 09:50:37 +09:00
virt irqchip/gic-v4.1: Move doorbell management to the GICv4 abstraction layer 2020-03-24 12:15:51 +00:00
.clang-format clang-format: Update with the latest for_each macro list 2020-03-06 21:50:05 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore selftest/lkdtm: Use local .gitignore 2020-03-02 08:39:39 -07:00
.mailmap media updates for v5.7-rc1 2020-03-30 13:42:05 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Hand MIPS over to Thomas 2020-02-24 22:43:18 -08:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next 2020-03-31 17:29:33 -07:00
Makefile Kbuild updates for v5.7 2020-03-31 16:03:39 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.