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David Hildenbrand c89357e27f mm: support GUP-triggered unsharing of anonymous pages
Whenever GUP currently ends up taking a R/O pin on an anonymous page that
might be shared -- mapped R/O and !PageAnonExclusive() -- any write fault
on the page table entry will end up replacing the mapped anonymous page
due to COW, resulting in the GUP pin no longer being consistent with the
page actually mapped into the page table.

The possible ways to deal with this situation are:
 (1) Ignore and pin -- what we do right now.
 (2) Fail to pin -- which would be rather surprising to callers and
     could break user space.
 (3) Trigger unsharing and pin the now exclusive page -- reliable R/O
     pins.

We want to implement 3) because it provides the clearest semantics and
allows for checking in unpin_user_pages() and friends for possible BUGs:
when trying to unpin a page that's no longer exclusive, clearly something
went very wrong and might result in memory corruptions that might be hard
to debug.  So we better have a nice way to spot such issues.

To implement 3), we need a way for GUP to trigger unsharing:
FAULT_FLAG_UNSHARE.  FAULT_FLAG_UNSHARE is only applicable to R/O mapped
anonymous pages and resembles COW logic during a write fault.  However, in
contrast to a write fault, GUP-triggered unsharing will, for example,
still maintain the write protection.

Let's implement FAULT_FLAG_UNSHARE by hooking into the existing write
fault handlers for all applicable anonymous page types: ordinary pages,
THP and hugetlb.

* If FAULT_FLAG_UNSHARE finds a R/O-mapped anonymous page that has been
  marked exclusive in the meantime by someone else, there is nothing to do.
* If FAULT_FLAG_UNSHARE finds a R/O-mapped anonymous page that's not
  marked exclusive, it will try detecting if the process is the exclusive
  owner. If exclusive, it can be set exclusive similar to reuse logic
  during write faults via page_move_anon_rmap() and there is nothing
  else to do; otherwise, we either have to copy and map a fresh,
  anonymous exclusive page R/O (ordinary pages, hugetlb), or split the
  THP.

This commit is heavily based on patches by Andrea.

Link: https://lkml.kernel.org/r/20220428083441.37290-16-david@redhat.com
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Co-developed-by: Andrea Arcangeli <aarcange@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Don Dutile <ddutile@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Khalid Aziz <khalid.aziz@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Liang Zhang <zhangliang5@huawei.com>
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nadav Amit <namit@vmware.com>
Cc: Oded Gabbay <oded.gabbay@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Roman Gushchin <guro@fb.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2022-05-09 18:20:45 -07:00
arch mm: use for_each_online_node and node_online instead of open coding 2022-04-29 14:36:58 -07:00
block block: don't print I/O error warning for dead disks 2022-04-15 06:33:03 -06:00
certs Kbuild updates for v5.18 2022-03-31 11:59:03 -07:00
crypto for-5.18/64bit-pi-2022-03-25 2022-03-26 12:01:35 -07:00
Documentation memcg: introduce per-memcg reclaim interface 2022-04-29 14:36:59 -07:00
drivers zram: add a huge_idle writeback mode 2022-04-29 14:36:59 -07:00
fs ksm: count ksm merging pages for each process 2022-04-28 23:16:16 -07:00
include mm: support GUP-triggered unsharing of anonymous pages 2022-05-09 18:20:45 -07:00
init Kbuild updates for v5.18 2022-03-31 11:59:03 -07:00
ipc fs: allocate inode by using alloc_inode_sb() 2022-03-22 15:57:03 -07:00
kernel mm/rmap: drop "compound" parameter from page_add_new_anon_rmap() 2022-05-09 18:20:43 -07:00
lib hex2bin: fix access beyond string end 2022-04-27 10:57:33 -07:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm mm: support GUP-triggered unsharing of anonymous pages 2022-05-09 18:20:45 -07:00
net tcp: fix F-RTO may not work correctly when receiving DSACK 2022-04-28 10:35:38 -07:00
samples dma-mapping updates for Linux 5.18 2022-03-29 08:50:14 -07:00
scripts hardening fixes for v5.18-rc3 2022-04-12 14:29:40 -10:00
security hardening updates for v5.18-rc1-fix1 2022-03-31 11:43:01 -07:00
sound ALSA: hda/realtek: Add quirk for Clevo NP70PNP 2022-04-21 21:23:47 +02:00
tools mm/page-flags: reuse PG_mappedtodisk as PG_anon_exclusive for PageAnon() pages 2022-05-09 18:20:44 -07:00
usr Kbuild updates for v5.18 2022-03-31 11:59:03 -07:00
virt KVM: SEV: add cache flush to solve SEV cache incoherency issues 2022-04-21 15:41:00 -04:00
.clang-format genirq/msi: Make interrupt allocation less convoluted 2021-12-16 22:22:20 +01:00
.cocciconfig
.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 .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: update Vasily Averin's email address 2022-04-08 14:20:36 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: replace a Microchip AT91 maintainer 2022-02-09 11:30:01 +01:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: add corresponding kselftests to memcg entry 2022-04-28 23:16:00 -07:00
Makefile Linux 5.18-rc4 2022-04-24 14:51:22 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

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.