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0274f9551e
Introduce ELF_HWCAP2 variable for x86 and reserve its bit 0 to expose the ring 3 MONITOR/MWAIT. HWCAP variables contain bitmasks which can be used by userspace applications to detect which 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. ELF_HWCAP2 type is u32 to be consistent with x86 ELF_HWCAP type. Signed-off-by: Grzegorz Andrejczuk <grzegorz.andrejczuk@intel.com> Cc: Piotr.Luc@intel.com Cc: dave.hansen@linux.intel.com Link: http://lkml.kernel.org/r/1484918557-15481-3-git-send-email-grzegorz.andrejczuk@intel.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de> |
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.