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| author | Borislav Petkov <bp@suse.de> | 2019-03-29 19:35:24 +0100 |
|---|---|---|
| committer | Borislav Petkov <bp@suse.de> | 2019-04-08 12:02:55 +0200 |
| commit | bfdd5a67c8cb02c147c6b012543e84cb1f5759ba (patch) | |
| tree | 81ff8cdc147d06d7084ee206c55ccb4e4a09dd88 /arch/x86/include | |
| parent | x86/uaccess: Fix implicit cast of __user pointer (diff) | |
| download | linux-bfdd5a67c8cb02c147c6b012543e84cb1f5759ba.tar.xz linux-bfdd5a67c8cb02c147c6b012543e84cb1f5759ba.zip | |
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.amit@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: x86@kernel.org
Link: https://lkml.kernel.org/r/20190330112022.28888-2-bp@alien8.de
Diffstat (limited to 'arch/x86/include')
| -rw-r--r-- | arch/x86/include/asm/cpufeature.h | 9 |
1 files 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) { |