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Peter Xu f5e59185b0 mm: don't skip swap entry even if zap_details specified 
commit 5abfd71d93 upstream.

Patch series "mm: Rework zap ptes on swap entries", v5.

Patch 1 should fix a long standing bug for zap_pte_range() on
zap_details usage.  The risk is we could have some swap entries skipped
while we should have zapped them.

Migration entries are not the major concern because file backed memory
always zap in the pattern that "first time without page lock, then
re-zap with page lock" hence the 2nd zap will always make sure all
migration entries are already recovered.

However there can be issues with real swap entries got skipped
errornoously.  There's a reproducer provided in commit message of patch
1 for that.

Patch 2-4 are cleanups that are based on patch 1.  After the whole
patchset applied, we should have a very clean view of zap_pte_range().

Only patch 1 needs to be backported to stable if necessary.

This patch (of 4):

The "details" pointer shouldn't be the token to decide whether we should
skip swap entries.

For example, when the callers specified details->zap_mapping==NULL, it
means the user wants to zap all the pages (including COWed pages), then
we need to look into swap entries because there can be private COWed
pages that was swapped out.

Skipping some swap entries when details is non-NULL may lead to wrongly
leaving some of the swap entries while we should have zapped them.

A reproducer of the problem:

===8<===
        #define _GNU_SOURCE         /* See feature_test_macros(7) */
        #include <stdio.h>
        #include <assert.h>
        #include <unistd.h>
        #include <sys/mman.h>
        #include <sys/types.h>

        int page_size;
        int shmem_fd;
        char *buffer;

        void main(void)
        {
                int ret;
                char val;

                page_size = getpagesize();
                shmem_fd = memfd_create("test", 0);
                assert(shmem_fd >= 0);

                ret = ftruncate(shmem_fd, page_size * 2);
                assert(ret == 0);

                buffer = mmap(NULL, page_size * 2, PROT_READ | PROT_WRITE,
                                MAP_PRIVATE, shmem_fd, 0);
                assert(buffer != MAP_FAILED);

                /* Write private page, swap it out */
                buffer[page_size] = 1;
                madvise(buffer, page_size * 2, MADV_PAGEOUT);

                /* This should drop private buffer[page_size] already */
                ret = ftruncate(shmem_fd, page_size);
                assert(ret == 0);
                /* Recover the size */
                ret = ftruncate(shmem_fd, page_size * 2);
                assert(ret == 0);

                /* Re-read the data, it should be all zero */
                val = buffer[page_size];
                if (val == 0)
                        printf("Good\n");
                else
                        printf("BUG\n");
        }
===8<===

We don't need to touch up the pmd path, because pmd never had a issue with
swap entries.  For example, shmem pmd migration will always be split into
pte level, and same to swapping on anonymous.

Add another helper should_zap_cows() so that we can also check whether we
should zap private mappings when there's no page pointer specified.

This patch drops that trick, so we handle swap ptes coherently.  Meanwhile
we should do the same check upon migration entry, hwpoison entry and
genuine swap entries too.

To be explicit, we should still remember to keep the private entries if
even_cows==false, and always zap them when even_cows==true.

The issue seems to exist starting from the initial commit of git.

[peterx@redhat.com: comment tweaks]
  Link: https://lkml.kernel.org/r/20220217060746.71256-2-peterx@redhat.com

Link: https://lkml.kernel.org/r/20220217060746.71256-1-peterx@redhat.com
Link: https://lkml.kernel.org/r/20220216094810.60572-1-peterx@redhat.com
Link: https://lkml.kernel.org/r/20220216094810.60572-2-peterx@redhat.com
Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Yang Shi <shy828301@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2022-04-13 20:59:27 +02:00
arch KVM: SVM: Allow AVIC support on system w/ physical APIC ID > 255 2022-04-13 20:59:25 +02:00
block block: Fix the maximum minor value is blk_alloc_ext_minor() 2022-04-08 14:24:11 +02:00
certs certs: Add support for using elliptic curve keys for signing modules 2021-08-23 19:55:42 +03:00
crypto crypto: xts - Add softdep on ecb 2022-04-08 14:23:55 +02:00
Documentation docs: sysctl/kernel: add missing bit to panic_print 2022-04-08 14:24:16 +02:00
drivers Revert "net/mlx5: Accept devlink user input after driver initialization complete" 2022-04-13 20:59:27 +02:00
fs btrfs: prevent subvol with swapfile from being deleted 2022-04-13 20:59:23 +02:00
include SUNRPC: Don't call connect() more than once on a TCP socket 2022-04-13 20:59:26 +02:00
init init/main.c: return 1 from handled __setup() functions 2022-04-13 20:59:10 +02:00
ipc ipc/sem: do not sleep with a spin lock held 2022-02-08 18:34:03 +01:00
kernel perf/core: Inherit event_caps 2022-04-13 20:59:24 +02:00
lib ubsan: remove CONFIG_UBSAN_OBJECT_SIZE 2022-04-13 20:59:27 +02:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm mm: don't skip swap entry even if zap_details specified 2022-04-13 20:59:27 +02:00
net SUNRPC: Don't call connect() more than once on a TCP socket 2022-04-13 20:59:26 +02:00
samples samples/bpf, xdpsock: Fix race when running for fix duration of time 2022-04-08 14:23:40 +02:00
scripts ubsan: remove CONFIG_UBSAN_OBJECT_SIZE 2022-04-13 20:59:27 +02:00
security Fix incorrect type in assignment of ipv6 port for audit 2022-04-08 14:23:55 +02:00
sound ASoC: topology: Allow TLV control to be either read or write 2022-04-08 14:24:15 +02:00
tools selftests: cgroup: Test open-time cgroup namespace usage for migration checks 2022-04-13 20:59:27 +02:00
usr usr/include/Makefile: add linux/nfc.h to the compile-test coverage 2022-02-01 17:27:15 +01:00
virt KVM: avoid NULL pointer dereference in kvm_dirty_ring_push 2022-04-13 20:59:26 +02:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.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: add Andrej Shadura 2021-10-18 20:22:03 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
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: adjust file entry for of_net.c after movement 2022-03-08 19:12:53 +01:00
Makefile Linux 5.15.33 2022-04-08 14:24:18 +02:00
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.