x86/PAT: Use try_cmpxchg() in set_page_memtype()

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Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
set_page_memtype.  x86 CMPXCHG instruction returns success in ZF flag,
so this change saves a compare after cmpxchg (and related move
instruction in front of cmpxchg).

Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg
fails. There is no need to re-read the value in the loop.

Note that the value from *ptr should be read using READ_ONCE to prevent
the compiler from merging, refetching or reordering the read.

No functional change intended.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230116163446.4734-1-ubizjak@gmail.com

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This commit is contained in:

Uros Bizjak 2023-01-16 17:34:46 +01:00 • committed by Ingo Molnar

parent 1d61659ced

commit 50fd4d5e69

1 changed files with 2 additions and 2 deletions

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arch/x86/mm/pat/memtype.c

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