diff options
| author | Borislav Petkov (AMD) <bp@alien8.de> | 2024-10-31 11:34:01 +0100 |
|---|---|---|
| committer | Borislav Petkov (AMD) <bp@alien8.de> | 2024-12-10 17:34:51 +0100 |
| commit | 4bf610499c429fa0bfb3fa94be450f01016224c5 (patch) | |
| tree | d619e6c1f1dc44cc3e0acd3403911d681ea33deb | |
| parent | 29188c16006176caee6cb6729103be51a29c1a93 (diff) | |
x86/cpufeature: Document cpu_feature_enabled() as the default to use
cpu_feature_enabled() should be used in most cases when CPU feature
support needs to be tested in code. Document that.
Reported-by: Sohil Mehta <sohil.mehta@intel.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Sohil Mehta <sohil.mehta@intel.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/r/20241031103401.GBZyNdGQ-ZyXKyzC_z@fat_crate.local
| -rw-r--r-- | arch/x86/include/asm/cpufeature.h | 18 |
1 files changed, 6 insertions, 12 deletions
diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h index 0b9611da6c53..de1ad09fe8d7 100644 --- a/arch/x86/include/asm/cpufeature.h +++ b/arch/x86/include/asm/cpufeature.h @@ -132,11 +132,12 @@ extern const char * const x86_bug_flags[NBUGINTS*32]; x86_this_cpu_test_bit(bit, cpu_info.x86_capability)) /* - * This macro is for detection of features which need kernel - * infrastructure to be used. It may *not* directly test the CPU - * itself. Use the cpu_has() family if you want true runtime - * testing of CPU features, like in hypervisor code where you are - * supporting a possible guest feature where host support for it + * This is the default CPU features testing macro to use in code. + * + * It is for detection of features which need kernel infrastructure to be + * used. It may *not* directly test the CPU itself. Use the cpu_has() family + * if you want true runtime testing of CPU features, like in hypervisor code + * where you are supporting a possible guest feature where host support for it * is not relevant. */ #define cpu_feature_enabled(bit) \ @@ -161,13 +162,6 @@ extern void clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int bit); #define setup_force_cpu_bug(bit) setup_force_cpu_cap(bit) /* - * 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. - * * Do not use an "m" constraint for [cap_byte] here: gcc doesn't know * that this is only used on a fallback path and will sometimes cause * it to manifest the address of boot_cpu_data in a register, fouling |