[PATCH v4 0/3] mm: Fix bug affecting swapping in MTE tagged pages

[Peter Collingbourne <pcc@google.com>]

This patch series reworks the logic that handles swapping in page
metadata to fix a reported bug [1] where metadata can sometimes not
be swapped in correctly after commit c145e0b47c77 ("mm: streamline COW
logic in do_swap_page()").

- Patch 1 fixes the bug itself, but still requires architectures
  to restore metadata in both arch_swap_restore() and set_pte_at().

- Patch 2 makes it so that architectures only need to restore metadata
  in arch_swap_restore().

- Patch 3 changes arm64 to remove support for restoring metadata
  in set_pte_at().

[1] https://lore.kernel.org/all/5050805753ac469e8d727c797c2218a9d780d434.camel@mediatek.com/

v4:
- Rebased onto v6.4-rc3
- Reverted change to arch/arm64/mm/mteswap.c; this change was not
  valid because swapcache pages can have arch_swap_restore() called
  on them multiple times

v3:
- Added patch to call arch_swap_restore() from unuse_pte()
- Rebased onto arm64/for-next/fixes

v2:
- Call arch_swap_restore() directly instead of via arch_do_swap_page()

Peter Collingbourne (3):
  mm: Call arch_swap_restore() from do_swap_page()
  mm: Call arch_swap_restore() from unuse_pte()
  arm64: mte: Simplify swap tag restoration logic

 arch/arm64/include/asm/mte.h     |  4 ++--
 arch/arm64/include/asm/pgtable.h | 14 ++----------
 arch/arm64/kernel/mte.c          | 37 ++++++--------------------------
 mm/memory.c                      |  7 ++++++
 mm/swapfile.c                    |  7 ++++++
 5 files changed, 25 insertions(+), 44 deletions(-)

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2.40.1.698.g37aff9b760-goog