diff options
author | Borislav Petkov (AMD) <bp@alien8.de> | 2025-04-09 13:14:35 +0200 |
---|---|---|
committer | Ingo Molnar <mingo@kernel.org> | 2025-04-09 13:56:52 +0200 |
commit | 254a6d14c9c952e8eae0fafd4fed3778721b948e (patch) | |
tree | 77f91bec5bfde2d13d1e1f94ed7661034f1a0c52 /Documentation | |
parent | af76f7d57ee9a3be7b3840595ce3e2bdedd594a7 (diff) |
Documentation/x86: Zap the subsection letters
The subsections already have numbering - no need for the letters too.
Zap the latter.
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20250409111435.GEZ_ZWmz3_lkP8S9Lb@fat_crate.local
Diffstat (limited to 'Documentation')
-rw-r--r-- | Documentation/arch/x86/cpuinfo.rst | 51 |
1 files changed, 29 insertions, 22 deletions
diff --git a/Documentation/arch/x86/cpuinfo.rst b/Documentation/arch/x86/cpuinfo.rst index 7114f34ba3e6..f80e2a558d2a 100644 --- a/Documentation/arch/x86/cpuinfo.rst +++ b/Documentation/arch/x86/cpuinfo.rst @@ -79,8 +79,9 @@ feature flags. How are feature flags created? ============================== -a: Feature flags can be derived from the contents of CPUID leaves. ------------------------------------------------------------------- +Feature flags can be derived from the contents of CPUID leaves +-------------------------------------------------------------- + These feature definitions are organized mirroring the layout of CPUID leaves and grouped in words with offsets as mapped in enum cpuid_leafs in cpufeatures.h (see arch/x86/include/asm/cpufeatures.h for details). @@ -89,8 +90,9 @@ cpufeatures.h, and if it is detected at run time, the flags will be displayed accordingly in /proc/cpuinfo. For example, the flag "avx2" comes from X86_FEATURE_AVX2 in cpufeatures.h. -b: Flags can be from scattered CPUID-based features. ----------------------------------------------------- +Flags can be from scattered CPUID-based features +------------------------------------------------ + Hardware features enumerated in sparsely populated CPUID leaves get software-defined values. Still, CPUID needs to be queried to determine if a given feature is present. This is done in init_scattered_cpuid_features(). @@ -104,8 +106,9 @@ has only one feature and would waste 31 bits of space in the x86_capability[] array. Since there is a struct cpuinfo_x86 for each possible CPU, the wasted memory is not trivial. -c: Flags can be created synthetically under certain conditions for hardware features. -------------------------------------------------------------------------------------- +Flags can be created synthetically under certain conditions for hardware features +--------------------------------------------------------------------------------- + Examples of conditions include whether certain features are present in MSR_IA32_CORE_CAPS or specific CPU models are identified. If the needed conditions are met, the features are enabled by the set_cpu_cap or @@ -114,8 +117,8 @@ the feature X86_FEATURE_SPLIT_LOCK_DETECT will be enabled and "split_lock_detect" will be displayed. The flag "ring3mwait" will be displayed only when running on INTEL_XEON_PHI_[KNL|KNM] processors. -d: Flags can represent purely software features. ------------------------------------------------- +Flags can represent purely software features +-------------------------------------------- These flags do not represent hardware features. Instead, they represent a software feature implemented in the kernel. For example, Kernel Page Table Isolation is purely software feature and its feature flag X86_FEATURE_PTI is @@ -130,8 +133,8 @@ x86_cap/bug_flags[] arrays in kernel/cpu/capflags.c. The names in the resulting x86_cap/bug_flags[] are used to populate /proc/cpuinfo. The naming of flags in the x86_cap/bug_flags[] are as follows: -a: Flags do not appear by default in /proc/cpuinfo --------------------------------------------------- +Flags do not appear by default in /proc/cpuinfo +----------------------------------------------- Feature flags are omitted by default from /proc/cpuinfo as it does not make sense for the feature to be exposed to userspace in most cases. For example, @@ -139,8 +142,8 @@ X86_FEATURE_ALWAYS is defined in cpufeatures.h but that flag is an internal kernel feature used in the alternative runtime patching functionality. So the flag does not appear in /proc/cpuinfo. -b: Specify a flag name if absolutely needed -------------------------------------------- +Specify a flag name if absolutely needed +---------------------------------------- If the comment on the line for the #define X86_FEATURE_* starts with a double-quote character (""), the string inside the double-quote characters @@ -155,25 +158,28 @@ shall override the new naming with the name already used in /proc/cpuinfo. Flags are missing when one or more of these happen ================================================== -a: The hardware does not enumerate support for it. --------------------------------------------------- +The hardware does not enumerate support for it +---------------------------------------------- + For example, when a new kernel is running on old hardware or the feature is not enabled by boot firmware. Even if the hardware is new, there might be a problem enabling the feature at run time, the flag will not be displayed. -b: The kernel does not know about the flag. -------------------------------------------- +The kernel does not know about the flag +--------------------------------------- + For example, when an old kernel is running on new hardware. -c: The kernel disabled support for it at compile-time. ------------------------------------------------------- +The kernel disabled support for it at compile-time +-------------------------------------------------- + For example, if 5-level-paging is not enabled when building (i.e., CONFIG_X86_5LEVEL is not selected) the flag "la57" will not show up [#f1]_. Even though the feature will still be detected via CPUID, the kernel disables it by clearing via setup_clear_cpu_cap(X86_FEATURE_LA57). -d: The feature is disabled at boot-time. ----------------------------------------- +The feature is disabled at boot-time +------------------------------------ A feature can be disabled either using a command-line parameter or because it failed to be enabled. The command-line parameter clearcpuid= can be used to disable features using the feature number as defined in @@ -186,8 +192,9 @@ disable specific features. The list of parameters includes, but is not limited to, nofsgsbase, nosgx, noxsave, etc. 5-level paging can also be disabled using "no5lvl". -e: The feature was known to be non-functional. ----------------------------------------------- +The feature was known to be non-functional +------------------------------------------ + The feature was known to be non-functional because a dependency was missing at runtime. For example, AVX flags will not show up if XSAVE feature is disabled since they depend on XSAVE feature. Another example would be broken |