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Merged
merged 3 commits into from
May 26, 2021

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TheSven73
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#273 introduced a build issue in the hwrng Rust driver. Fixed. Added that driver to the CI to prevent this from happening in the future.

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ojeda commented May 26, 2021

Conflicts -- otherwise LGTM!

@TheSven73 TheSven73 force-pushed the rust-for-linux-ci-defconfig branch from 0b7dab0 to 07de3a4 Compare May 26, 2021 15:53
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v1 -> v2

Rebased to avoid merge conflict.

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ojeda commented May 26, 2021

Hmm... the first commit removes most of the config.

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Hmm... the first commit removes most of the config.

I believe it's correct. There are two ways to create a defconfig:

  1. simply copy .config
  2. run make savedefconfig which generates a file called defconfig

Method (1) creates a defconfig that explicitly contains every setting. Method (2) leaves out those settings that are equal to their default (indicated in Kconfig).

What happened here, is that a verbose defconfig was replaced by a short defconfig.

Should this be split into an extra commit? Or keep verbose defconfig ? The latter makes diffing much harder.

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ojeda commented May 26, 2021

If we are going for the short configs, we should do that in another PR, updating all the arches at once.

So for the moment, please keep the long ones to be consistent.

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Sure, but it will get messy. Adding support for the BCM2835 chip will probably add a lot of extra defconfig items. They're all equal to their defaults, but will nevertheless show up in the diff.

Sven Van Asbroeck added 3 commits May 26, 2021 15:44
This ensures that the driver gets built as part of CI.

Signed-off-by: Sven Van Asbroeck <thesven73@gmail.com>
Fix build error from Rust-for-Linux#273 ("rust: CStr overhaul").

Signed-off-by: Sven Van Asbroeck <thesven73@gmail.com>
Some non-existent dts files were left in the `Makefile` by a previous
PR. Remove them.

Signed-off-by: Sven Van Asbroeck <thesven73@gmail.com>
@TheSven73 TheSven73 force-pushed the rust-for-linux-ci-defconfig branch from 07de3a4 to d656610 Compare May 26, 2021 19:46
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Review of d6566105835d:

  • ✔️ Commit 4266a32: Looks fine!
  • ✔️ Commit 6d7443c: Looks fine!
  • ✔️ Commit d656610: Looks fine!

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v2 -> v3

ojeda: Commit defconfigs using the verbose method.

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ojeda commented May 26, 2021

It doesn't look that bad! Thanks!

By the way, it does not really matter for us, but normally I would put the fix first, and then enable it in the CI second (otherwise, if we had a CI that compiled all commits -- like we may in the future, it would be an error).

@ojeda ojeda merged commit 7fde08b into Rust-for-Linux:rust May 26, 2021
@TheSven73 TheSven73 deleted the rust-for-linux-ci-defconfig branch May 26, 2021 20:19
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Yes, very good point, I'll make sure that happens in the future. Thanks for the merge ! 💯

dakr pushed a commit that referenced this pull request Mar 10, 2025
userfaultfd_move() checks whether the PTE entry is present or a
swap entry.

- If the PTE entry is present, move_present_pte() handles folio
  migration by setting:

  src_folio->index = linear_page_index(dst_vma, dst_addr);

- If the PTE entry is a swap entry, move_swap_pte() simply copies
  the PTE to the new dst_addr.

This approach is incorrect because, even if the PTE is a swap entry,
it can still reference a folio that remains in the swap cache.

This creates a race window between steps 2 and 4.
 1. add_to_swap: The folio is added to the swapcache.
 2. try_to_unmap: PTEs are converted to swap entries.
 3. pageout: The folio is written back.
 4. Swapcache is cleared.
If userfaultfd_move() occurs in the window between steps 2 and 4,
after the swap PTE has been moved to the destination, accessing the
destination triggers do_swap_page(), which may locate the folio in
the swapcache. However, since the folio's index has not been updated
to match the destination VMA, do_swap_page() will detect a mismatch.

This can result in two critical issues depending on the system
configuration.

If KSM is disabled, both small and large folios can trigger a BUG
during the add_rmap operation due to:

 page_pgoff(folio, page) != linear_page_index(vma, address)

[   13.336953] page: refcount:6 mapcount:1 mapping:00000000f43db19c index:0xffffaf150 pfn:0x4667c
[   13.337520] head: order:2 mapcount:1 entire_mapcount:0 nr_pages_mapped:1 pincount:0
[   13.337716] memcg:ffff00000405f000
[   13.337849] anon flags: 0x3fffc0000020459(locked|uptodate|dirty|owner_priv_1|head|swapbacked|node=0|zone=0|lastcpupid=0xffff)
[   13.338630] raw: 03fffc0000020459 ffff80008507b538 ffff80008507b538 ffff000006260361
[   13.338831] raw: 0000000ffffaf150 0000000000004000 0000000600000000 ffff00000405f000
[   13.339031] head: 03fffc0000020459 ffff80008507b538 ffff80008507b538 ffff000006260361
[   13.339204] head: 0000000ffffaf150 0000000000004000 0000000600000000 ffff00000405f000
[   13.339375] head: 03fffc0000000202 fffffdffc0199f01 ffffffff00000000 0000000000000001
[   13.339546] head: 0000000000000004 0000000000000000 00000000ffffffff 0000000000000000
[   13.339736] page dumped because: VM_BUG_ON_PAGE(page_pgoff(folio, page) != linear_page_index(vma, address))
[   13.340190] ------------[ cut here ]------------
[   13.340316] kernel BUG at mm/rmap.c:1380!
[   13.340683] Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP
[   13.340969] Modules linked in:
[   13.341257] CPU: 1 UID: 0 PID: 107 Comm: a.out Not tainted 6.14.0-rc3-gcf42737e247a-dirty #299
[   13.341470] Hardware name: linux,dummy-virt (DT)
[   13.341671] pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[   13.341815] pc : __page_check_anon_rmap+0xa0/0xb0
[   13.341920] lr : __page_check_anon_rmap+0xa0/0xb0
[   13.342018] sp : ffff80008752bb20
[   13.342093] x29: ffff80008752bb20 x28: fffffdffc0199f00 x27: 0000000000000001
[   13.342404] x26: 0000000000000000 x25: 0000000000000001 x24: 0000000000000001
[   13.342575] x23: 0000ffffaf0d0000 x22: 0000ffffaf0d0000 x21: fffffdffc0199f00
[   13.342731] x20: fffffdffc0199f00 x19: ffff000006210700 x18: 00000000ffffffff
[   13.342881] x17: 6c203d2120296567 x16: 6170202c6f696c6f x15: 662866666f67705f
[   13.343033] x14: 6567617028454741 x13: 2929737365726464 x12: ffff800083728ab0
[   13.343183] x11: ffff800082996bf8 x10: 0000000000000fd7 x9 : ffff80008011bc40
[   13.343351] x8 : 0000000000017fe8 x7 : 00000000fffff000 x6 : ffff8000829eebf8
[   13.343498] x5 : c0000000fffff000 x4 : 0000000000000000 x3 : 0000000000000000
[   13.343645] x2 : 0000000000000000 x1 : ffff0000062db980 x0 : 000000000000005f
[   13.343876] Call trace:
[   13.344045]  __page_check_anon_rmap+0xa0/0xb0 (P)
[   13.344234]  folio_add_anon_rmap_ptes+0x22c/0x320
[   13.344333]  do_swap_page+0x1060/0x1400
[   13.344417]  __handle_mm_fault+0x61c/0xbc8
[   13.344504]  handle_mm_fault+0xd8/0x2e8
[   13.344586]  do_page_fault+0x20c/0x770
[   13.344673]  do_translation_fault+0xb4/0xf0
[   13.344759]  do_mem_abort+0x48/0xa0
[   13.344842]  el0_da+0x58/0x130
[   13.344914]  el0t_64_sync_handler+0xc4/0x138
[   13.345002]  el0t_64_sync+0x1ac/0x1b0
[   13.345208] Code: aa1503e0 f000f801 910f6021 97ff5779 (d4210000)
[   13.345504] ---[ end trace 0000000000000000 ]---
[   13.345715] note: a.out[107] exited with irqs disabled
[   13.345954] note: a.out[107] exited with preempt_count 2

If KSM is enabled, Peter Xu also discovered that do_swap_page() may
trigger an unexpected CoW operation for small folios because
ksm_might_need_to_copy() allocates a new folio when the folio index
does not match linear_page_index(vma, addr).

This patch also checks the swapcache when handling swap entries. If a
match is found in the swapcache, it processes it similarly to a present
PTE.
However, there are some differences. For example, the folio is no longer
exclusive because folio_try_share_anon_rmap_pte() is performed during
unmapping.
Furthermore, in the case of swapcache, the folio has already been
unmapped, eliminating the risk of concurrent rmap walks and removing the
need to acquire src_folio's anon_vma or lock.

Note that for large folios, in the swapcache handling path, we directly
return -EBUSY since split_folio() will return -EBUSY regardless if
the folio is under writeback or unmapped. This is not an urgent issue,
so a follow-up patch may address it separately.

[v-songbaohua@oppo.com: minor cleanup according to Peter Xu]
  Link: https://lkml.kernel.org/r/20250226024411.47092-1-21cnbao@gmail.com
Link: https://lkml.kernel.org/r/20250226001400.9129-1-21cnbao@gmail.com
Fixes: adef440 ("userfaultfd: UFFDIO_MOVE uABI")
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
Acked-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jann Horn <jannh@google.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Lokesh Gidra <lokeshgidra@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Nicolas Geoffray <ngeoffray@google.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: ZhangPeng <zhangpeng362@huawei.com>
Cc: Tangquan Zheng <zhengtangquan@oppo.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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