Messages in this thread Patch in this message | | | From | Borislav Petkov <> | Subject | [PATCH 1/5] x86/asm: Clarify static_cpu_has()'s intended use | Date | Sat, 30 Mar 2019 12:20:18 +0100 |
| |
From: Borislav Petkov <bp@suse.de>
Clarify when one should use static_cpu_has() and when one should use boot_cpu_has().
Requested-by: Nadav Amit <nadav.amit@gmail.com> Signed-off-by: Borislav Petkov <bp@suse.de> Cc: x86@kernel.org --- 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 30cf12c81db3..1d337c51f7e6 100644 --- a/arch/x86/include/asm/cpufeature.h +++ b/arch/x86/include/asm/cpufeature.h @@ -156,9 +156,12 @@ 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) { -- 2.21.0
| |