Commit-ID: bfdd5a67c8cb02c147c6b012543e84cb1f5759ba Gitweb: https://git.kernel.org/tip/bfdd5a67c8cb02c147c6b012543e84cb1f5759ba Author: Borislav Petkov <b...@suse.de> AuthorDate: Fri, 29 Mar 2019 19:35:24 +0100 Committer: Borislav Petkov <b...@suse.de> CommitDate: Mon, 8 Apr 2019 12:02:55 +0200
x86/asm: Clarify static_cpu_has()'s intended use Clarify when one should use static_cpu_has() and when one should use boot_cpu_has(). Requested-by: Nadav Amit <nadav.a...@gmail.com> Signed-off-by: Borislav Petkov <b...@suse.de> Cc: x...@kernel.org Link: https://lkml.kernel.org/r/20190330112022.28888-2...@alien8.de --- arch/x86/include/asm/cpufeature.h | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h index 2fb791a1b479..6d6d5cc4302b 100644 --- a/arch/x86/include/asm/cpufeature.h +++ b/arch/x86/include/asm/cpufeature.h @@ -155,9 +155,12 @@ extern void clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int bit); #else /* - * Static testing of CPU features. Used the same as boot_cpu_has(). - * These will statically patch the target code for additional - * performance. + * Static testing of CPU features. Used the same as boot_cpu_has(). It + * statically patches the target code for additional performance. Use + * static_cpu_has() only in fast paths, where every cycle counts. Which + * means that the boot_cpu_has() variant is already fast enough for the + * majority of cases and you should stick to using it as it is generally + * only two instructions: a RIP-relative MOV and a TEST. */ static __always_inline bool _static_cpu_has(u16 bit) {
