From: Uros Bizjak Date: Mon, 16 Jan 2023 16:34:46 +0000 (+0100) Subject: x86/PAT: Use try_cmpxchg() in set_page_memtype() X-Git-Tag: v6.3-rc1~200^2~3 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=50fd4d5e6914b60ea6f89c2cbff7a07799414c62;p=thirdparty%2Flinux.git 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: Uros Bizjak Signed-off-by: Ingo Molnar Link: https://lore.kernel.org/r/20230116163446.4734-1-ubizjak@gmail.com --- diff --git a/arch/x86/mm/pat/memtype.c b/arch/x86/mm/pat/memtype.c index fb4b1b5e0deab..6d1ba2dda35d6 100644 --- a/arch/x86/mm/pat/memtype.c +++ b/arch/x86/mm/pat/memtype.c @@ -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)