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David Hildenbrand d74943a2f3 mm/gup: reintroduce FOLL_NUMA as FOLL_HONOR_NUMA_FAULT 
Unfortunately commit 474098edac ("mm/gup: replace FOLL_NUMA by
gup_can_follow_protnone()") missed that follow_page() and
follow_trans_huge_pmd() never implicitly set FOLL_NUMA because they really
don't want to fail on PROT_NONE-mapped pages -- either due to NUMA hinting
or due to inaccessible (PROT_NONE) VMAs.

As spelled out in commit 0b9d705297 ("mm: numa: Support NUMA hinting
page faults from gup/gup_fast"): "Other follow_page callers like KSM
should not use FOLL_NUMA, or they would fail to get the pages if they use
follow_page instead of get_user_pages."

liubo reported [1] that smaps_rollup results are imprecise, because they
miss accounting of pages that are mapped PROT_NONE.  Further, it's easy to
reproduce that KSM no longer works on inaccessible VMAs on x86-64, because
pte_protnone()/pmd_protnone() also indictaes "true" in inaccessible VMAs,
and follow_page() refuses to return such pages right now.

As KVM really depends on these NUMA hinting faults, removing the
pte_protnone()/pmd_protnone() handling in GUP code completely is not
really an option.

To fix the issues at hand, let's revive FOLL_NUMA as FOLL_HONOR_NUMA_FAULT
to restore the original behavior for now and add better comments.

Set FOLL_HONOR_NUMA_FAULT independent of FOLL_FORCE in
is_valid_gup_args(), to add that flag for all external GUP users.

Note that there are three GUP-internal __get_user_pages() users that don't
end up calling is_valid_gup_args() and consequently won't get
FOLL_HONOR_NUMA_FAULT set.

1) get_dump_page(): we really don't want to handle NUMA hinting
   faults. It specifies FOLL_FORCE and wouldn't have honored NUMA
   hinting faults already.
2) populate_vma_page_range(): we really don't want to handle NUMA hinting
   faults. It specifies FOLL_FORCE on accessible VMAs, so it wouldn't have
   honored NUMA hinting faults already.
3) faultin_vma_page_range(): we similarly don't want to handle NUMA
   hinting faults.

To make the combination of FOLL_FORCE and FOLL_HONOR_NUMA_FAULT work in
inaccessible VMAs properly, we have to perform VMA accessibility checks in
gup_can_follow_protnone().

As GUP-fast should reject such pages either way in
pte_access_permitted()/pmd_access_permitted() -- for example on x86-64 and
arm64 that both implement pte_protnone() -- let's just always fallback to
ordinary GUP when stumbling over pte_protnone()/pmd_protnone().

As Linus notes [2], honoring NUMA faults might only make sense for
selected GUP users.

So we should really see if we can instead let relevant GUP callers specify
it manually, and not trigger NUMA hinting faults from GUP as default. 
Prepare for that by making FOLL_HONOR_NUMA_FAULT an external GUP flag and
adding appropriate documenation.

While at it, remove a stale comment from follow_trans_huge_pmd(): That
comment for pmd_protnone() was added in commit 2b4847e730 ("mm: numa:
serialise parallel get_user_page against THP migration"), which noted:

	THP does not unmap pages due to a lack of support for migration
	entries at a PMD level.  This allows races with get_user_pages

Nowadays, we do have PMD migration entries, so the comment no longer
applies.  Let's drop it.

[1] https://lore.kernel.org/r/20230726073409.631838-1-liubo254@huawei.com
[2] https://lore.kernel.org/r/CAHk-=wgRiP_9X0rRdZKT8nhemZGNateMtb366t37d8-x7VRs=g@mail.gmail.com

Link: https://lkml.kernel.org/r/20230803143208.383663-2-david@redhat.com
Fixes: 474098edac ("mm/gup: replace FOLL_NUMA by gup_can_follow_protnone()")
Signed-off-by: David Hildenbrand <david@redhat.com>
Reported-by: liubo <liubo254@huawei.com>
Closes: https://lore.kernel.org/r/20230726073409.631838-1-liubo254@huawei.com
Reported-by: Peter Xu <peterx@redhat.com>
Closes: https://lore.kernel.org/all/ZMKJjDaqZ7FW0jfe@x1n/
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Peter Xu <peterx@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
2023-08-21 13:07:20 -07:00
arch x86: 2023-07-30 11:19:08 -07:00
block block-6.5-2023-07-21 2023-07-22 11:05:15 -07:00
certs KEYS: Add missing function documentation 2023-04-24 16:15:52 +03:00
crypto crypto: algif_hash - Fix race between MORE and non-MORE sends 2023-07-08 22:48:42 +10:00
Documentation TTY/Serial fixes for 6.5-rc4 2023-07-30 11:51:36 -07:00
drivers spi: Fixes for v6.5 2023-07-30 12:54:31 -07:00
fs nilfs2: fix use-after-free of nilfs_root in dirtying inodes via iput 2023-08-04 13:03:43 -07:00
include mm/gup: reintroduce FOLL_NUMA as FOLL_HONOR_NUMA_FAULT 2023-08-21 13:07:20 -07:00
init Kbuild updates for v6.5 2023-07-01 09:24:31 -07:00
io_uring io_uring-6.5-2023-07-28 2023-07-28 10:19:44 -07:00
ipc Merge branch 'work.namespace' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2023-02-24 19:20:07 -08:00
kernel Probe fixes for 6.5-rc3: 2023-07-30 11:27:22 -07:00
lib crypto, cifs: fix error handling in extract_iter_to_sg() 2023-08-04 13:03:40 -07:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm mm/gup: reintroduce FOLL_NUMA as FOLL_HONOR_NUMA_FAULT 2023-08-21 13:07:20 -07:00
net A patch to reduce the potential for erroneous RBD exclusive lock 2023-07-28 10:47:24 -07:00
rust rust: error: impl Debug for Error with errname() integration 2023-06-13 01:24:42 +02:00
samples arm64: ftrace: Add direct call trampoline samples support 2023-07-10 17:51:54 -04:00
scripts x86: 2023-07-30 11:19:08 -07:00
security security: keys: perform capable check only on privileged operations 2023-07-28 18:07:41 +00:00
sound ASoC: Fixes for v6.5 2023-07-27 14:54:23 +02:00
tools selftests: cgroup: fix test_kmem_basic false positives 2023-08-04 13:03:42 -07:00
usr initramfs: Encode dependency on KBUILD_BUILD_TIMESTAMP 2023-06-06 17:54:49 +09:00
virt KVM: Grab a reference to KVM for VM and vCPU stats file descriptors 2023-07-29 11:05:28 -04:00
.clang-format iommu: Add for_each_group_device() 2023-05-23 08:15:51 +02:00
.cocciconfig
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore Revert ".gitignore: ignore *.cover and *.mbx" 2023-07-04 15:05:12 -07:00
.mailmap mailmap: update remaining active codeaurora.org email addresses 2023-07-27 13:07:05 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS - Address -Wmissing-prototype warnings 2023-06-26 16:43:54 -07:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: add maple tree mailing list 2023-08-04 13:03:42 -07:00
Makefile Linux 6.5-rc4 2023-07-30 13:23:47 -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.