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Thu, 31 Oct 2024 10:34:02 +0000 (UTC) Date: Thu, 31 Oct 2024 11:34:01 +0100 From: Borislav Petkov To: Sohil Mehta Cc: Yazen Ghannam , "Luck, Tony" , Andy Whitcroft , Joe Perches , "linux-edac@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "x86@kernel.org" , "avadhut.naik@amd.com" , "john.allen@amd.com" , "mario.limonciello@amd.com" , "bhelgaas@google.com" , "Shyam-sundar.S-k@amd.com" , "richard.gong@amd.com" , "jdelvare@suse.com" , "linux@roeck-us.net" , "clemens@ladisch.de" , "hdegoede@redhat.com" , "ilpo.jarvinen@linux.intel.com" , "linux-pci@vger.kernel.org" , "linux-hwmon@vger.kernel.org" , "platform-driver-x86@vger.kernel.org" , "naveenkrishna.chatradhi@amd.com" , "carlos.bilbao.osdev@gmail.com" Subject: [PATCH] x86/cpufeature: Document cpu_feature_enabled() as the default to use Message-ID: <20241031103401.GBZyNdGQ-ZyXKyzC_z@fat_crate.local> References: <20241023172150.659002-1-yazen.ghannam@amd.com> <20241023172150.659002-4-yazen.ghannam@amd.com> <20241025155830.GQZxvAJkJnfLfNpSRx@fat_crate.local> <20241029143928.GA1011322@yaz-khff2.amd.com> <20241029150847.GLZyD6f-Hk6pRTEt2c@fat_crate.local> <20241030142138.GA1304646@yaz-khff2.amd.com> Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: From: "Borislav Petkov (AMD)" 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 Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Sohil Mehta --- arch/x86/include/asm/cpufeature.h | 18 ++++++------------ 1 file 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