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Peter Xu d3cb86e633 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>
2022-04-20 09:08:30 +02:00
arch arm64: patch_text: Fixup last cpu should be master 2022-04-20 09:08:30 +02:00
block block: bio-integrity: Advance seed correctly for larger interval sizes 2022-02-08 18:16:28 +01:00
certs
crypto crypto: authenc - Fix sleep in atomic context in decrypt_tail 2022-04-20 09:08:12 +02:00
Documentation Documentation: update stable tree link 2022-04-20 09:08:09 +02:00
drivers dmaengine: Revert "dmaengine: shdma: Fix runtime PM imbalance on error" 2022-04-20 09:08:30 +02:00
firmware
fs btrfs: fix qgroup reserve overflow the qgroup limit 2022-04-20 09:08:30 +02:00
include net: add missing SOF_TIMESTAMPING_OPT_ID support 2022-04-20 09:08:28 +02:00
init init/main.c: return 1 from handled __setup() functions 2022-04-20 09:08:28 +02:00
ipc ipc: WARN if trying to remove ipc object which is absent 2021-12-08 08:46:53 +01:00
kernel printk: fix return value of printk.devkmsg __setup handler 2022-04-20 09:08:15 +02:00
lib lib/test: use after free in register_test_dev_kmod() 2022-04-20 09:08:21 +02:00
mm mm: don't skip swap entry even if zap_details specified 2022-04-20 09:08:30 +02:00
net net: add missing SOF_TIMESTAMPING_OPT_ID support 2022-04-20 09:08:28 +02:00
samples samples/kretprobes: Fix return value if register_kretprobe() failed 2021-11-26 11:40:31 +01:00
scripts Makefile.extrawarn: Move -Wunaligned-access to W=1 2022-02-23 11:57:32 +01:00
security Fix incorrect type in assignment of ipv6 port for audit 2022-04-20 09:08:21 +02:00
sound ASoC: topology: Allow TLV control to be either read or write 2022-04-20 09:08:25 +02:00
tools tools build: Use $(shell ) instead of `` to get embedded libperl's ccopts 2022-04-20 09:08:30 +02:00
usr
virt KVM: Prevent module exit until all VMs are freed 2022-04-20 09:08:24 +02:00
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Makefile Linux 4.14.275 2022-04-02 12:41:10 +02:00
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