Introduce ELF_HWCAP2 variable for x86 and reserve its bit 0 to expose the ring 3 MONITOR/MWAIT.
HWCAP variables contain bitmask which can be used by userspace applications to detect what instruction sets are supported by CPU. On x86 architecture information about CPU capabilities can be checked via CPUID instructions, unfortunately presence of ring 3 MONITOR/MWAIT feature cannot be checked this way. ELF_HWCAP cannot be used as well, because on x86 it is set to CPUID[1].EDX which means that all bits are reserved there. HWCAP2 approach was chosen because it reuses existing solution present in other architectures, so only minor modifications are required to the kernel and userspace applications. When ELF_HWCAP2 is defined kernel maps it to AT_HWCAP2 during the start of the application. This way the ring 3 MONITOR/MWAIT feature can be detected using getauxval() API in a simple and fast manner. Signed-off-by: Grzegorz Andrejczuk <grzegorz.andrejc...@intel.com> --- arch/x86/include/asm/elf.h | 9 +++++++++ arch/x86/include/uapi/asm/hwcap2.h | 7 +++++++ arch/x86/kernel/cpu/common.c | 3 +++ 3 files changed, 19 insertions(+) create mode 100644 arch/x86/include/uapi/asm/hwcap2.h diff --git a/arch/x86/include/asm/elf.h b/arch/x86/include/asm/elf.h index e7f155c..59703aa 100644 --- a/arch/x86/include/asm/elf.h +++ b/arch/x86/include/asm/elf.h @@ -258,6 +258,15 @@ extern int force_personality32; #define ELF_HWCAP (boot_cpu_data.x86_capability[CPUID_1_EDX]) +extern unsigned int elf_hwcap2; + +/* + * HWCAP2 supplies mask with kernel enabled CPU features, so that + * the application can discover that it can safely use them. + * The bits are defined in uapi/asm/hwcap2.h. + */ +#define ELF_HWCAP2 elf_hwcap2 + /* This yields a string that ld.so will use to load implementation specific libraries for optimization. This is more specific in intent than poking at uname or /proc/cpuinfo. diff --git a/arch/x86/include/uapi/asm/hwcap2.h b/arch/x86/include/uapi/asm/hwcap2.h new file mode 100644 index 0000000..0bd2be5 --- /dev/null +++ b/arch/x86/include/uapi/asm/hwcap2.h @@ -0,0 +1,7 @@ +#ifndef _ASM_X86_HWCAP2_H +#define _ASM_X86_HWCAP2_H + +/* MONITOR/MWAIT enabled in Ring 3 */ +#define HWCAP2_RING3MWAIT (1 << 0) + +#endif diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index cc9e980..217697b 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -35,6 +35,7 @@ #include <asm/desc.h> #include <asm/fpu/internal.h> #include <asm/mtrr.h> +#include <asm/hwcap2.h> #include <linux/numa.h> #include <asm/asm.h> #include <asm/bugs.h> @@ -51,6 +52,8 @@ #include "cpu.h" +unsigned int elf_hwcap2 __read_mostly; + /* all of these masks are initialized in setup_cpu_local_masks() */ cpumask_var_t cpu_initialized_mask; cpumask_var_t cpu_callout_mask; -- 2.5.1