arch/x86/cpuinfo.rst

11 in arch/x86/include/asm/cpufeatures.h. If the kernel cares about a feature
12 or KVM want to expose the feature to a KVM guest, it can and should have
16 If users want to know if a feature is available on a given system, they
19 If such flag represents a hardware feature, it also means that the
25 can explain missing flags: the expected feature failed to enable, the feature
26 is missing in hardware, platform firmware did not enable it, the feature is
28 not support the feature and thus has not enabled it. In general, /proc/cpuinfo
32 How are feature flags created?
37 These feature definitions are organized mirroring the layout of CPUID
40 If a feature is defined with a X86_FEATURE_<name> definition in
49 if a given feature is present. This is done in init_scattered_cpuid_features().
56 has only one feature and would waste 31 bits of space in the x86_capability[]
66 the feature X86_FEATURE_SPLIT_LOCK_DETECT will be enabled and
73 software feature implemented in the kernel. For example, Kernel Page Table
74 Isolation is purely software feature and its feature flag X86_FEATURE_PTI is
106 The feature shall be omitted from /proc/cpuinfo if it does not make sense for
107 the feature to be exposed to userspace. For example, X86_FEATURE_ALWAYS is
108 defined in cpufeatures.h but that flag is an internal kernel feature used
117 For example, when a new kernel is running on old hardware or the feature is
119 problem enabling the feature at run time, the flag will not be displayed.
129 Even though the feature will still be detected via CPUID, the kernel disables
132 d: The feature is disabled at boot-time.
134 A feature can be disabled either using a command-line parameter or because
136 to disable features using the feature number as defined in
146 e: The feature was known to be non-functional.
148 The feature was known to be non-functional because a dependency was
149 missing at runtime. For example, AVX flags will not show up if XSAVE feature
150 is disabled since they depend on XSAVE feature. Another example would be broken
152 enable a feature.