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No need to call maybe_mkwrite() to then wrprotect if the source PMD was not
writable.
It's worth nothing that this now allows for PTEs to be writable even if
the source PMD was not writable: if vma->vm_page_prot includes write
permissions.
As documented in commit 931298e103c2 ("mm/userfaultfd: rely on
vma->vm_page_prot in uffd_wp_range()"), any mechanism that intends to
have pages wrprotected (COW, writenotify, mprotect, uffd-wp, softdirty,
...) has to properly adjust vma->vm_page_prot upfront, to not include
write permissions. If vma->vm_page_prot includes write permissions, the
PTE/PMD can be writable as default.
This now mimics the handling in mm/migrate.c:remove_migration_pte() and in
mm/huge_memory.c:remove_migration_pmd(), which has been in place for a
long time (except that 96a9c287e25d ("mm/migrate: fix wrongly apply write
bit after mkdirty on sparc64") temporarily changed it).
Link: https://lkml.kernel.org/r/20230411142512.438404-7-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Hugh Dickins <hughd@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This reverts commit 624a2c94f5b7 ("Partly revert "mm/thp: carry over dirty
bit when thp splits on pmd"") and the fixup in commit e833bc503405
("mm/thp: re-apply mkdirty for small pages after split").
Now that sparc64 mkdirty handling is fixed and no longer sets a PTE/PMD
writable that shouldn't be writable, let's revert the temporary fix and
remove the stale comment.
The mkdirty mm selftest still passes with this change on sparc64.
Note that loongarch handling was fixed in commit bf2f34a506e6 ("LoongArch:
Set _PAGE_DIRTY only if _PAGE_WRITE is set in {pmd,pte}_mkdirty()")
Link: https://lkml.kernel.org/r/20230411142512.438404-6-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Hugh Dickins <hughd@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This reverts commit 96a9c287e25d ("mm/migrate: fix wrongly apply write bit
after mkdirty on sparc64").
Now that sparc64 mkdirty handling is fixed and no longer sets a PTE/PMD
writable that shouldn't be writable, let's revert the temporary fix.
The mkdirty mm selftest still passes with this change on sparc64.
Note that loongarch handling was fixed in commit bf2f34a506e6 ("LoongArch:
Set _PAGE_DIRTY only if _PAGE_WRITE is set in {pmd,pte}_mkdirty()").
Link: https://lkml.kernel.org/r/20230411142512.438404-5-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Hugh Dickins <hughd@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
On sparc64, there is no HW modified bit, therefore, SW tracks via a SW bit
if the PTE is dirty via pte_mkdirty(). However, pte_mkdirty() currently
also unconditionally sets the HW writable bit, which is wrong.
pte_mkdirty() is not supposed to make a PTE actually writable, unless the
SW writable bit -- pte_write() -- indicates that the PTE is not
write-protected. Fortunately, sparc64 also defines a SW writable bit.
For example, this already turned into a problem in the context of THP
splitting as documented in commit 624a2c94f5b7 ("Partly revert "mm/thp:
carry over dirty bit when thp splits on pmd""), and for page migration, as
documented in commit 96a9c287e25d ("mm/migrate: fix wrongly apply write
bit after mkdirty on sparc64").
Also, we might want to use the dirty PTE bit in the context of KSM with
shared zeropage [1], whereby setting the page writable would be
problematic.
But more general, any code that might end up setting a PTE/PMD dirty
inside a VM without write permissions is possibly broken,
Before this commit (sun4u in QEMU):
root@debian:~/linux/tools/testing/selftests/mm# ./mkdirty
# [INFO] detected THP size: 8192 KiB
TAP version 13
1..6
# [INFO] PTRACE write access
not ok 1 SIGSEGV generated, page not modified
# [INFO] PTRACE write access to THP
not ok 2 SIGSEGV generated, page not modified
# [INFO] Page migration
ok 3 SIGSEGV generated, page not modified
# [INFO] Page migration of THP
ok 4 SIGSEGV generated, page not modified
# [INFO] PTE-mapping a THP
ok 5 SIGSEGV generated, page not modified
# [INFO] UFFDIO_COPY
not ok 6 SIGSEGV generated, page not modified
Bail out! 3 out of 6 tests failed
# Totals: pass:3 fail:3 xfail:0 xpass:0 skip:0 error:0
Test #3,#4,#5 pass ever since we added some MM workarounds, the
underlying issue remains.
Let's fix the remaining issues and prepare for reverting the workarounds
by setting the HW writable bit only if both, the SW dirty bit and the SW
writable bit are set.
We have to move pte_dirty() and pte_write() up. The code patching
mechanism and handling constants > 22bit is a bit special on sparc64.
The ASM logic in pte_mkdirty() and pte_mkwrite() match the logic in
pte_mkold() to create the mask depending on the machine type. The ASM
logic in __pte_mkhwwrite() matches the logic in pte_present(), just
using an "or" instead of an "and" instruction.
With this commit (sun4u in QEMU):
root@debian:~/linux/tools/testing/selftests/mm# ./mkdirty
# [INFO] detected THP size: 8192 KiB
TAP version 13
1..6
# [INFO] PTRACE write access
ok 1 SIGSEGV generated, page not modified
# [INFO] PTRACE write access to THP
ok 2 SIGSEGV generated, page not modified
# [INFO] Page migration
ok 3 SIGSEGV generated, page not modified
# [INFO] Page migration of THP
ok 4 SIGSEGV generated, page not modified
# [INFO] PTE-mapping a THP
ok 5 SIGSEGV generated, page not modified
# [INFO] UFFDIO_COPY
ok 6 SIGSEGV generated, page not modified
# Totals: pass:6 fail:0 xfail:0 xpass:0 skip:0 error:0
This handling seems to have been in place forever.
[1] https://lkml.kernel.org/r/533a7c3d-3a48-b16b-b421-6e8386e0b142@redhat.com
Link: https://lkml.kernel.org/r/20230411142512.438404-4-david@redhat.com
Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Hugh Dickins <hughd@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Let's add some tests that trigger (pte|pmd)_mkdirty on VMAs without write
permissions. If an architecture implementation is wrong, we might
accidentally set the PTE/PMD writable and allow for write access in a VMA
without write permissions.
The tests include reproducers for the two issues recently discovered
and worked-around in core-MM for now:
(1) commit 624a2c94f5b7 ("Partly revert "mm/thp: carry over dirty
bit when thp splits on pmd"")
(2) commit 96a9c287e25d ("mm/migrate: fix wrongly apply write bit
after mkdirty on sparc64")
In addition, some other tests that reveal further issues.
All tests pass under x86_64:
./mkdirty
# [INFO] detected THP size: 2048 KiB
TAP version 13
1..6
# [INFO] PTRACE write access
ok 1 SIGSEGV generated, page not modified
# [INFO] PTRACE write access to THP
ok 2 SIGSEGV generated, page not modified
# [INFO] Page migration
ok 3 SIGSEGV generated, page not modified
# [INFO] Page migration of THP
ok 4 SIGSEGV generated, page not modified
# [INFO] PTE-mapping a THP
ok 5 SIGSEGV generated, page not modified
# [INFO] UFFDIO_COPY
ok 6 SIGSEGV generated, page not modified
# Totals: pass:6 fail:0 xfail:0 xpass:0 skip:0 error:0
But some fail on sparc64:
./mkdirty
# [INFO] detected THP size: 8192 KiB
TAP version 13
1..6
# [INFO] PTRACE write access
not ok 1 SIGSEGV generated, page not modified
# [INFO] PTRACE write access to THP
not ok 2 SIGSEGV generated, page not modified
# [INFO] Page migration
ok 3 SIGSEGV generated, page not modified
# [INFO] Page migration of THP
ok 4 SIGSEGV generated, page not modified
# [INFO] PTE-mapping a THP
ok 5 SIGSEGV generated, page not modified
# [INFO] UFFDIO_COPY
not ok 6 SIGSEGV generated, page not modified
Bail out! 3 out of 6 tests failed
# Totals: pass:3 fail:3 xfail:0 xpass:0 skip:0 error:0
Reverting both above commits makes all tests fail on sparc64:
./mkdirty
# [INFO] detected THP size: 8192 KiB
TAP version 13
1..6
# [INFO] PTRACE write access
not ok 1 SIGSEGV generated, page not modified
# [INFO] PTRACE write access to THP
not ok 2 SIGSEGV generated, page not modified
# [INFO] Page migration
not ok 3 SIGSEGV generated, page not modified
# [INFO] Page migration of THP
not ok 4 SIGSEGV generated, page not modified
# [INFO] PTE-mapping a THP
not ok 5 SIGSEGV generated, page not modified
# [INFO] UFFDIO_COPY
not ok 6 SIGSEGV generated, page not modified
Bail out! 6 out of 6 tests failed
# Totals: pass:0 fail:6 xfail:0 xpass:0 skip:0 error:0
The tests are useful to detect other problematic archs, to verify new
arch fixes, and to stop such issues from reappearing in the future.
For now, we don't add any hugetlb tests.
Link: https://lkml.kernel.org/r/20230411142512.438404-3-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Hugh Dickins <hughd@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "mm: (pte|pmd)_mkdirty() should not unconditionally allow for
write access".
This is the follow-up on [1], adding selftests (testing for known issues
we added workarounds for and other issues that haven't been fixed yet),
fixing sparc64, reverting the workarounds, and perform one cleanup.
The patch from [1] was modified slightly (updated/extended patch
description, dropped one unnecessary NOP instruction from the ASM in
__pte_mkhwwrite()).
Retested on x86_64 and sparc64 (sun4u in QEMU).
I scanned most architectures to make sure their (pte|pmd)_mkdirty()
handling is correct. To be sure, we can run the selftests and find out if
other architectures are still affectes (loongarch was fixed recently as
well).
Based on master for now. I don't expect surprises regarding mm-tress, but
I can rebase if there are any problems.
This patch (of 6):
The COW selftest can deal with THP not being configured. So move error
handling of read_pmd_pagesize() into the callers such that we can reuse it
in the COW selftest.
Link: https://lkml.kernel.org/r/20230411142512.438404-1-david@redhat.com
Link: https://lkml.kernel.org/r/20221212130213.136267-1-david@redhat.com [1]
Link: https://lkml.kernel.org/r/20230411142512.438404-2-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Hugh Dickins <hughd@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Propagate read errors to the caller instead of dropping them on the floor,
and stop returning the somewhat dangerous 1 on success from
read_from_bdev*.
Link: https://lkml.kernel.org/r/20230411171459.567614-18-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Currently nothing waits for the synchronous reads before accessing the
data. Switch them to an on-stack bio and submit_bio_wait to make sure the
I/O has actually completed when the work item has been flushed. This also
removes the call to page_endio that would unlock a page that has never
been locked.
Drop the partial_io/sync flag, as chaining only makes sense for the
asynchronous reads of the entire page.
Link: https://lkml.kernel.org/r/20230411171459.567614-17-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
bio_alloc will never return a NULL bio when it is allowed to sleep, and
adding a single page to bio with a single vector also can't fail, so
switch to the asserting __bio_add_page variant and drop the error returns.
Link: https://lkml.kernel.org/r/20230411171459.567614-16-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
read_from_bdev always reads a whole page, so pass a page to it instead of
the bvec and remove the now pointless zram_bvec_read_from_bdev wrapper.
Link: https://lkml.kernel.org/r/20230411171459.567614-15-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Split the read/modify/write case into a separate helper.
Link: https://lkml.kernel.org/r/20230411171459.567614-14-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
__zram_bvec_write only extracts the page from __zram_bvec_write and always
expects a full page of input. Pass the page directly instead of the bvec
and rename the function to zram_write_page.
Link: https://lkml.kernel.org/r/20230411171459.567614-13-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Split the partial read into a separate helper.
Link: https://lkml.kernel.org/r/20230411171459.567614-12-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
writeback_store always reads a full page, so just call zram_read_page
directly and bypass the boune buffer handling.
Link: https://lkml.kernel.org/r/20230411171459.567614-11-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
__zram_bvec_read doesn't get passed a bvec, but always read a whole page.
Rename it to make the usage more clear.
Link: https://lkml.kernel.org/r/20230411171459.567614-10-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
There is no point in allocation a highmem page when we instantly need to
copy from it.
Link: https://lkml.kernel.org/r/20230411171459.567614-9-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Instead of having an outer loop in __zram_make_request and then branch out
for reads vs writes for each loop iteration in zram_bvec_rw, split the
main handler into separat zram_bio_read and zram_bio_write handlers that
also include the functionality formerly in zram_bvec_rw.
Link: https://lkml.kernel.org/r/20230411171459.567614-8-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
When the low-level access fails, don't clear the idle flag or clear the
caches, and just return.
Link: https://lkml.kernel.org/r/20230411171459.567614-7-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Switch on the bio operation in zram_submit_bio and only call into
__zram_make_request for read and write operations.
Link: https://lkml.kernel.org/r/20230411171459.567614-6-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
bio_for_each_segment synthetize bvecs that never cross page boundaries, so
don't duplicate that work in an inner loop.
Link: https://lkml.kernel.org/r/20230411171459.567614-5-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Derive the index and offset variables inside the function, and complete
the bio directly in preparation for cleaning up the I/O path.
Link: https://lkml.kernel.org/r/20230411171459.567614-4-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
All bios hande to drivers from the block layer are checked against the
device size and for logical block alignment already (and have been since
long before zram was merged), so don't duplicate those checks.
Link: https://lkml.kernel.org/r/20230411171459.567614-3-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "zram I/O path cleanups and fixups", v3.
This series cleans up the zram I/O path, and fixes the handling of
synchronous I/O to the underlying device in the writeback_store function
or for > 4K PAGE_SIZE systems.
The fixes are at the end, as I could not fully reason about them being
safe before untangling the callchain.
This patch (of 17):
read_from_bdev_sync is currently only compiled for non-4k PAGE_SIZE, which
means it won't be built with the most common configurations.
Replace the ifdef with a check for the PAGE_SIZE in an if instead. The
check uses an extra symbol and IS_ENABLED to allow the compiler to
eliminate the dead code, leading to the same generated code size:
text data bss dec hex filename
16709 1428 12 18149 46e5 drivers/block/zram/zram_drv.o.old
16709 1428 12 18149 46e5 drivers/block/zram/zram_drv.o.new
Link: https://lkml.kernel.org/r/20230411171459.567614-1-hch@lst.de
Link: https://lkml.kernel.org/r/20230411171459.567614-2-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Add a test case to check whether the number of maple_alloc structures is
actually equal to mas->alloc->total.
Link: https://lkml.kernel.org/r/20230411041005.26205-2-zhangpeng.00@bytedance.com
Signed-off-by: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Liam R. Howlett <Liam.Howlett@Oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
smatch reports
mm/backing-dev.c:266:1: warning: symbol
'dev_attr_min_bytes' was not declared. Should it be static?
mm/backing-dev.c:294:1: warning: symbol
'dev_attr_max_bytes' was not declared. Should it be static?
These variables are only used in one file so should be static.
Link: https://lkml.kernel.org/r/20230408141609.2703647-1-trix@redhat.com
Signed-off-by: Tom Rix <trix@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
The type of variable pointed to by pivs is unsigned long, but the type
used in sizeof is a pointer type. Change it to unsigned long.
This change has no runtime effect, as sizeof(ul) == sizeof(ul *).
Link: https://lkml.kernel.org/r/20230411023513.15227-1-zhangpeng.00@bytedance.com
Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Signed-off-by: Peng Zhang <zhangpeng.00@bytedance.com>
Reported-by: David Binderman <dcb314@hotmail.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Convert mfill_atomic_pte_copy(), shmem_mfill_atomic_pte() and
mfill_atomic_pte() to take in a folio pointer.
Convert mfill_atomic() to use a folio. Convert page_kaddr to kaddr in
mfill_atomic().
Link: https://lkml.kernel.org/r/20230410133932.32288-7-zhangpeng362@huawei.com
Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Replace copy_user_huge_page() with copy_user_large_folio().
copy_user_large_folio() does the same as copy_user_huge_page(), but takes
in folios instead of pages. Remove pages_per_huge_page from
copy_user_large_folio(), because we can get that from folio_nr_pages(dst).
Convert copy_user_gigantic_page() to take in folios.
Link: https://lkml.kernel.org/r/20230410133932.32288-6-zhangpeng362@huawei.com
Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Convert hugetlb_mfill_atomic_pte() to take in a folio pointer instead of
a page pointer.
Convert mfill_atomic_hugetlb() to use a folio.
Link: https://lkml.kernel.org/r/20230410133932.32288-5-zhangpeng362@huawei.com
Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>
Reviewed-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Replace copy_huge_page_from_user() with copy_folio_from_user().
copy_folio_from_user() does the same as copy_huge_page_from_user(), but
takes in a folio instead of a page.
Convert page_kaddr to kaddr in copy_folio_from_user() to do indenting
cleanup.
Link: https://lkml.kernel.org/r/20230410133932.32288-4-zhangpeng362@huawei.com
Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>
Reviewed-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
kmap() and kmap_atomic() are being deprecated in favor of
kmap_local_page() which is appropriate for any thread local context.[1]
Let's replace the kmap() and kmap_atomic() with kmap_local_page() in
copy_huge_page_from_user(). When allow_pagefault is false, disable page
faults to prevent potential deadlock.[2]
[1] https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@intel.com/
[2] https://lkml.kernel.org/r/20221025220136.2366143-1-ira.weiny@intel.com
Link: https://lkml.kernel.org/r/20230410133932.32288-3-zhangpeng362@huawei.com
Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "userfaultfd: convert userfaultfd functions to use folios",
v6.
This patch series converts several userfaultfd functions to use folios.
This patch (of 6):
Call vma_alloc_folio() directly instead of alloc_page_vma() and convert
page_kaddr to kaddr in mfill_atomic_pte_copy(). Removes several calls to
compound_head().
Link: https://lkml.kernel.org/r/20230410133932.32288-1-zhangpeng362@huawei.com
Link: https://lkml.kernel.org/r/20230410133932.32288-2-zhangpeng362@huawei.com
Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>
Reviewed-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Cc: Vishal Moola (Oracle) <vishal.moola@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
When !CONFIG_SHMEM smaps_shmem_walk_ops is defined but not used,
triggering a compiler warning. To avoid the warning remove the #ifdef
around the usage. This has no effect because shmem_mapping() is a stub
returning false when !CONFIG_SHMEM so the code will be compiled out,
however we now need to also provide a stub for shmem_swap_usage().
Link: https://lkml.kernel.org/r/20230405103819.151246-1-steven.price@arm.com
Fixes: 7b86ac3371b7 ("pagewalk: separate function pointers from iterator data")
Signed-off-by: Steven Price <steven.price@arm.com>
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/oe-kbuild-all/202304031749.UiyJpxzF-lkp@intel.com/
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Commit 700d2e9a36b9 ("mm, page_alloc: reduce page alloc/free sanity
checks") has introduced a new static key check_pages_enabled to control
when struct pages are sanity checked during allocation and freeing. Mel
Gorman suggested that free_tail_pages_check() could use this static key as
well, instead of relying on CONFIG_DEBUG_VM. That makes sense, so do
that. Also rename the function to free_tail_page_prepare() because it
works on a single tail page and has a struct page preparation component as
well as the optional checking component.
Also remove some unnecessary unlikely() within static_branch_unlikely()
statements that Mel pointed out for commit 700d2e9a36b9.
Link: https://lkml.kernel.org/r/20230405142840.11068-1-vbabka@suse.cz
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Suggested-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Alexander Halbuer <halbuer@sra.uni-hannover.de>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
If we end up with a writable migration entry that has the uffd-wp bit set,
we already messed up: the source PTE/PMD was writable, which means we
could have modified the page without notifying uffd first. Setting the
uffd-wp bit always implies converting migration entries to !writable
migration entries.
Commit 8f34f1eac382 ("mm/userfaultfd: fix uffd-wp special cases for
fork()") documents that "3. Forget to carry over uffd-wp bit for a write
migration huge pmd entry", but it doesn't really say why that should be
relevant.
So let's remove that code to avoid hiding an eventual underlying issue (in
the future, we might want to warn when creating writable migration entries
that have the uffd-wp bit set -- or even better when turning a PTE
writable that still has the uffd-wp bit set).
This now matches the handling for hugetlb migration entries in
hugetlb_change_protection().
In copy_huge_pmd()/copy_nonpresent_pte()/copy_hugetlb_page_range(), we
still transfer the uffd-bit also for writable migration entries, but
simply because we have unified handling for "writable" and
"readable-exclusive" migration entries, and we care about transferring the
uffd-wp bit for the latter.
Link: https://lkml.kernel.org/r/20230405160236.587705-3-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Since we have updated mlock to use folios, it's better to call
folios_put() instead of calling release_pages() directly.
Link: https://lkml.kernel.org/r/20230405161854.6931-2-zhengqi.arch@bytedance.com
Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
If a library wants to get information from auxv (for instance,
AT_HWCAP/AT_HWCAP2), it has a few options, none of them perfectly reliable
or ideal:
- Be main or the pre-main startup code, and grub through the stack above
main. Doesn't work for a library.
- Call libc getauxval. Not ideal for libraries that are trying to be
libc-independent and/or don't otherwise require anything from other
libraries.
- Open and read /proc/self/auxv. Doesn't work for libraries that may run
in arbitrarily constrained environments that may not have /proc
mounted (e.g. libraries that might be used by an init program or a
container setup tool).
- Assume you're on the main thread and still on the original stack, and
try to walk the stack upwards, hoping to find auxv. Extremely bad
idea.
- Ask the caller to pass auxv in for you. Not ideal for a user-friendly
library, and then your caller may have the same problem.
Add a prctl that copies current->mm->saved_auxv to a userspace buffer.
Link: https://lkml.kernel.org/r/d81864a7f7f43bca6afa2a09fc2e850e4050ab42.1680611394.git.josh@joshtriplett.org
Signed-off-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Simplify code of mas_wr_node_walk() without changing functionality, and
improve readability. Remove some special judgments. Instead of
dynamically recording the min and max in the loop, get the final min and
max directly at the end.
Link: https://lkml.kernel.org/r/20230314124203.91572-3-zhangpeng.00@bytedance.com
Signed-off-by: Peng Zhang <zhangpeng.00@bytedance.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
As noticed by Geert, commit b5c88f21531c ("microblaze/mm: support
__HAVE_ARCH_PTE_SWP_EXCLUSIVE") modified m68k code by accident. While
replacing 0x080 by CF_PAGE_NOCACHE is correct, although it should have
been part of commit ed4154067a08 ("m68k/mm: support
__HAVE_ARCH_PTE_SWP_EXCLUSIVE"), replacing "bit 7" by "bit 24" in the
comment was wrong.
Let's revert to the previous, correct, comment.
Link: https://lkml.kernel.org/r/20230404085636.121409-1-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Using vma_lookup() verifies the address is contained in the found vma.
This results in easier to read the code.
Link: https://lkml.kernel.org/r/20230404094515.1883552-1-zhangpeng362@huawei.com
Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
cgroups v1 has a unique way of setting up memory pressure notifications:
the user opens "memory.pressure_level" of the cgroup they want to monitor
for pressure, then open "cgroup.event_control" and write the fd (among
other things) to that file. memory.pressure_level has no other use,
specifically it does not support any read or write operations.
Consequently, no handlers are provided, and cgroup_file_mode() sets the
permissions to 000. However, to actually use the mechanism, the
subscribing user must have read access to the file and open the fd for
reading, see memcg_write_event_control().
This is all fine as long as the subscribing process runs as root and is
otherwise unconfined by further restrictions. However, if you add strict
access controls such as selinux, the permission bits will be enforced, and
opening memory.pressure_level for reading will fail, preventing the
process from subscribing, even as root.
To work around this issue, introduce a dummy read handler. When
memory.pressure_level is created, cgroup_file_mode() will notice the
existence of a handler, and therefore add read permissions to the file.
Link: https://lkml.kernel.org/r/20230404105900.2005-1-flosch@nutanix.com
Signed-off-by: Florian Schmidt <flosch@nutanix.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Make sure that collapse_file doesn't interfere with checking the uptodate
flag in the page cache by only inserting hpage into the page cache after
it has been updated and marked uptodate. This is achieved by simply not
replacing present pages with hpage when iterating over the target range.
The present pages are already locked, so replacing them with the locked
hpage before the collapse is finalized is unnecessary. However, it is
necessary to stop freezing the present pages after validating them, since
leaving long-term frozen pages in the page cache can lead to deadlocks.
Simply checking the reference count is sufficient to ensure that there are
no long-term references hanging around that would the collapse would
break. Similar to hpage, there is no reason that the present pages
actually need to be frozen in addition to being locked.
This fixes a race where folio_seek_hole_data would mistake hpage for an
fallocated but unwritten page. This race is visible to userspace via data
temporarily disappearing from SEEK_DATA/SEEK_HOLE. This also fixes a
similar race where pages could temporarily disappear from mincore.
Link: https://lkml.kernel.org/r/20230404120117.2562166-5-stevensd@google.com
Fixes: f3f0e1d2150b ("khugepaged: add support of collapse for tmpfs/shmem pages")
Signed-off-by: David Stevens <stevensd@chromium.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jiaqi Yan <jiaqiyan@google.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Make sure that collapse_file respects any userfaultfds registered with
MODE_MISSING. If userspace has any such userfaultfds registered, then for
any page which it knows to be missing, it may expect a
UFFD_EVENT_PAGEFAULT. This means collapse_file needs to be careful when
collapsing a shmem range would result in replacing an empty page with a
THP, to avoid breaking userfaultfd.
Synchronization when checking for userfaultfds in collapse_file is tricky
because the mmap locks can't be used to prevent races with the
registration of new userfaultfds. Instead, we provide synchronization by
ensuring that userspace cannot observe the fact that pages are missing
before we check for userfaultfds. Although this allows registration of a
userfaultfd to race with collapse_file, it ensures that userspace cannot
observe any pages transition from missing to present after such a race
occurs. This makes such a race indistinguishable to the collapse
occurring immediately before the userfaultfd registration.
The first step to provide this synchronization is to stop filling gaps
during the loop iterating over the target range, since the page cache lock
can be dropped during that loop. The second step is to fill the gaps with
XA_RETRY_ENTRY after the page cache lock is acquired the final time, to
avoid races with accesses to the page cache that only take the RCU read
lock.
The fact that we don't fill holes during the initial iteration means that
collapse_file now has to handle faults occurring during the collapse.
This is done by re-validating the number of missing pages after acquiring
the page cache lock for the final time.
This fix is targeted at khugepaged, but the change also applies to
MADV_COLLAPSE. MADV_COLLAPSE on a range with a userfaultfd will now
return EBUSY if there are any missing pages (instead of succeeding on
shmem and returning EINVAL on anonymous memory). There is also now a
window during MADV_COLLAPSE where a fault on a missing page will cause the
syscall to fail with EAGAIN.
The fact that intermediate page cache state can no longer be observed
before the rollback of a failed collapse is also technically a
userspace-visible change (via at least SEEK_DATA and SEEK_END), but it is
exceedingly unlikely that anything relies on being able to observe that
transient state.
Link: https://lkml.kernel.org/r/20230404120117.2562166-4-stevensd@google.com
Signed-off-by: David Stevens <stevensd@chromium.org>
Acked-by: Peter Xu <peterx@redhat.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jiaqi Yan <jiaqiyan@google.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Add a rollback label to deal with failure, instead of continuously
checking for RESULT_SUCCESS, to make it easier to add more failure cases.
The refactoring also allows the collapse_file tracepoint to include hpage
on success (instead of NULL).
Link: https://lkml.kernel.org/r/20230404120117.2562166-3-stevensd@google.com
Signed-off-by: David Stevens <stevensd@chromium.org>
Acked-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jiaqi Yan <jiaqiyan@google.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "mm/khugepaged: fixes for khugepaged+shmem", v6.
This series reworks collapse_file so that the intermediate state of the
collapse does not leak out of collapse_file. Although this makes
collapse_file a bit more complicated, it means that the rest of the
kernel doesn't have to deal with the unusual state. This directly fixes
races with both lseek and mincore.
This series also fixes the fact that khugepaged completely breaks
userfaultfd+shmem. The rework of collapse_file provides a convenient
place to check for registered userfaultfds without making the shmem
userfaultfd implementation care about khugepaged.
Finally, this series adds a lru_add_drain after swapping in shmem pages,
which makes the subsequent folio_isolate_lru significantly more likely to
succeed.
This patch (of 4):
Call lru_add_drain after swapping in shmem pages so that isolate_lru_page
is more likely to succeed.
Link: https://lkml.kernel.org/r/20230404120117.2562166-1-stevensd@google.com
Link: https://lkml.kernel.org/r/20230404120117.2562166-2-stevensd@google.com
Signed-off-by: David Stevens <stevensd@chromium.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jiaqi Yan <jiaqiyan@google.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Peter Xu <peterx@redhat.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Make collapse_file roll back when copying pages failed. More concretely:
- extract copying operations into a separate loop
- postpone the updates for nr_none until both scanning and copying
succeeded
- postpone joining small xarray entries until both scanning and copying
succeeded
- postpone the update operations to NR_XXX_THPS until both scanning and
copying succeeded
- for non-SHMEM file, roll back filemap_nr_thps_inc if scan succeeded but
copying failed
Tested manually:
0. Enable khugepaged on system under test. Mount tmpfs at /mnt/ramdisk.
1. Start a two-thread application. Each thread allocates a chunk of
non-huge memory buffer from /mnt/ramdisk.
2. Pick 4 random buffer address (2 in each thread) and inject
uncorrectable memory errors at physical addresses.
3. Signal both threads to make their memory buffer collapsible, i.e.
calling madvise(MADV_HUGEPAGE).
4. Wait and then check kernel log: khugepaged is able to recover from
poisoned pages by skipping them.
5. Signal both threads to inspect their buffer contents and make sure no
data corruption.
Link: https://lkml.kernel.org/r/20230329151121.949896-4-jiaqiyan@google.com
Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: David Stevens <stevensd@chromium.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Tong Tiangen <tongtiangen@huawei.com>
Cc: Tony Luck <tony.luck@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Similar to how copy_mc_user_highpage is implemented for copy_user_highpage
on #MC supported architecture, introduce the #MC handled version of
copy_highpage.
This helper has immediate usage when khugepaged wants to copy file-backed
memory pages and tolerate #MC.
Link: https://lkml.kernel.org/r/20230329151121.949896-3-jiaqiyan@google.com
Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Cc: David Stevens <stevensd@chromium.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Tong Tiangen <tongtiangen@huawei.com>
Cc: Tony Luck <tony.luck@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Problem
=======
Memory DIMMs are subject to multi-bit flips, i.e. memory errors. As
memory size and density increase, the chances of and number of memory
errors increase. The increasing size and density of server RAM in the
data center and cloud have shown increased uncorrectable memory errors.
There are already mechanisms in the kernel to recover from uncorrectable
memory errors. This series of patches provides the recovery mechanism for
the particular kernel agent khugepaged when it collapses memory pages.
Impact
======
The main reason we chose to make khugepaged collapsing tolerant of memory
failures was its high possibility of accessing poisoned memory while
performing functionally optional compaction actions. Standard
applications typically don't have strict requirements on the size of its
pages. So they are given 4K pages by the kernel. The kernel is able to
improve application performance by either
1) giving applications 2M pages to begin with, or
2) collapsing 4K pages into 2M pages when possible.
This collapsing operation is done by khugepaged, a kernel agent that is
constantly scanning memory. When collapsing 4K pages into a 2M page, it
must copy the data from the 4K pages into a physically contiguous 2M page.
Therefore, as long as there exists one poisoned cache line in collapsible
4K pages, khugepaged will eventually access it. The current impact to
users is a machine check exception triggered kernel panic. However,
khugepaged’s compaction operations are not functionally required kernel
actions. Therefore making khugepaged tolerant to poisoned memory will
greatly improve user experience.
This patch series is for cases where khugepaged is the first guy that
detects the memory errors on the poisoned pages. IOW, the pages are not
known to have memory errors when khugepaged collapsing gets to them. In
our observation, this happens frequently when the huge page ratio of the
system is relatively low, which is fairly common in virtual machines
running on cloud.
Solution
========
As stated before, it is less desirable to crash the system only because
khugepaged accesses poisoned pages while it is collapsing 4K pages. The
high level idea of this patch series is to skip the group of pages
(usually 512 4K-size pages) once khugepaged finds one of them is poisoned,
as these pages have become ineligible to be collapsed.
We are also careful to unwind operations khuagepaged has performed before
it detects memory failures. For example, before copying and collapsing a
group of anonymous pages into a huge page, the source pages will be
isolated and their page table is unlinked from their PMD. These
operations need to be undone in order to ensure these pages are not
changed/lost from the perspective of other threads (both user and kernel
space). As for file backed memory pages, there already exists a rollback
case. This patch just extends it so that khugepaged also correctly rolls
back when it fails to copy poisoned 4K pages.
This patch (of 3):
Make __collapse_huge_page_copy return whether copying anonymous pages
succeeded, and make collapse_huge_page handle the return status.
Break existing PTE scan loop into two for-loops. The first loop copies
source pages into target huge page, and can fail gracefully when running
into memory errors in source pages. If copying all pages succeeds, the
second loop releases and clears up these normal pages. Otherwise, the
second loop rolls back the page table and page states by:
- re-establishing the original PTEs-to-PMD connection.
- releasing source pages back to their LRU list.
Tested manually:
0. Enable khugepaged on system under test.
1. Start a two-thread application. Each thread allocates a chunk of
non-huge anonymous memory buffer.
2. Pick 4 random buffer locations (2 in each thread) and inject
uncorrectable memory errors at corresponding physical addresses.
3. Signal both threads to make their memory buffer collapsible, i.e.
calling madvise(MADV_HUGEPAGE).
4. Wait and check kernel log: khugepaged is able to recover from poisoned
pages and skips collapsing them.
5. Signal both threads to inspect their buffer contents and make sure no
data corruption.
Link: https://lkml.kernel.org/r/20230329151121.949896-1-jiaqiyan@google.com
Link: https://lkml.kernel.org/r/20230329151121.949896-2-jiaqiyan@google.com
Signed-off-by: Jiaqi Yan <jiaqiyan@google.com>
Cc: David Stevens <stevensd@chromium.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Tong Tiangen <tongtiangen@huawei.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
In some situations, we may end up calling memcg_rstat_updated() with a
value of 0, which means the stat was not actually updated. An example is
if we fail to reclaim any pages in shrink_folio_list().
Do not add the cgroup to the rstat updated tree in this case, to avoid
unnecessarily flushing it.
Link: https://lkml.kernel.org/r/20230330191801.1967435-9-yosryahmed@google.com
Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Acked-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Reviewed-by: Michal Koutný <mkoutny@suse.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vasily Averin <vasily.averin@linux.dev>
Cc: Zefan Li <lizefan.x@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Memory reclaim is a sleepable context. Flushing is an expensive operaiton
that scales with the number of cpus and the number of cgroups in the
system, so avoid doing it atomically unnecessarily. This can slow down
reclaim code if flushing stats is taking too long, but there is already
multiple cond_resched()'s in reclaim code.
Link: https://lkml.kernel.org/r/20230330191801.1967435-8-yosryahmed@google.com
Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Acked-by: Shakeel Butt <shakeelb@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vasily Averin <vasily.averin@linux.dev>
Cc: Zefan Li <lizefan.x@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
