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authorBorislav Petkov <bp@suse.de>2019-03-29 19:35:24 +0100
committerBorislav Petkov <bp@suse.de>2019-04-08 12:02:55 +0200
commitbfdd5a67c8cb02c147c6b012543e84cb1f5759ba (patch)
tree81ff8cdc147d06d7084ee206c55ccb4e4a09dd88 /arch/x86/include/asm/cpufeature.h
parenta6cbfbe6677efb5ca47bb7958c2718236c25126e (diff)
downloadlinux-bfdd5a67c8cb02c147c6b012543e84cb1f5759ba.tar.bz2
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/asm/cpufeature.h')
-rw-r--r--arch/x86/include/asm/cpufeature.h9
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)
{