Commit 50fd4d5e authored by Uros Bizjak's avatar Uros Bizjak Committed by Ingo Molnar
Browse files

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



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: default avatarUros Bizjak <ubizjak@gmail.com>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230116163446.4734-1-ubizjak@gmail.com
parent 1d61659c

arch/x86/mm/pat/memtype.c

+2 −2
Original line number Diff line number Diff line
@@ -159,10 +159,10 @@ static inline void set_page_memtype(struct page *pg, 
		break;

	}



	old_flags = READ_ONCE(pg->flags);

	do {

		old_flags = pg->flags;

		new_flags = (old_flags & _PGMT_CLEAR_MASK) | memtype_flags;

	} while (cmpxchg(&pg->flags, old_flags, new_flags) != old_flags);

	} while (!try_cmpxchg(&pg->flags, &old_flags, new_flags));

}

#else

static inline enum page_cache_mode get_page_memtype(struct page *pg)