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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
hifive-unleashed-5.2
Borislav Petkov 2019-03-29 19:35:24 +01:00
parent a6cbfbe667
commit bfdd5a67c8
1 changed files with 6 additions and 3 deletions
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9
arch/x86/include/asm/cpufeature.h
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@ -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)
{