[PATCH 1/2] Documentation/x86: Update the naming of CPU features for /proc/cpuinfo

[Borislav Petkov]

From: "Naveen N Rao (AMD)" <naveen@xxxxxxxxxx>
Date: Wed, 9 Apr 2025 12:42:45 +0200

Commit

  78ce84b9e0a5 ("x86/cpufeatures: Flip the /proc/cpuinfo appearance logic")

changed how CPU feature names should be specified. Update document to
reflect the same.

Signed-off-by: Naveen N Rao (AMD) <naveen@xxxxxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
---
 Documentation/arch/x86/cpuinfo.rst | 28 ++++++++++++----------------
 1 file changed, 12 insertions(+), 16 deletions(-)

diff --git a/Documentation/arch/x86/cpuinfo.rst b/Documentation/arch/x86/cpuinfo.rst
index 6ef426a52cdc..7114f34ba3e6 100644
--- a/Documentation/arch/x86/cpuinfo.rst
+++ b/Documentation/arch/x86/cpuinfo.rst
@@ -130,14 +130,18 @@ 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: The name of the flag is from the string in X86_FEATURE_<name> by default.
-----------------------------------------------------------------------------
-By default, the flag <name> in /proc/cpuinfo is extracted from the respective
-X86_FEATURE_<name> in cpufeatures.h. For example, the flag "avx2" is from
-X86_FEATURE_AVX2.
-
-b: The naming can be overridden.
---------------------------------
+a: 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,
+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
+-------------------------------------------
+
 If the comment on the line for the #define X86_FEATURE_* starts with a
 double-quote character (""), the string inside the double-quote characters
 will be the name of the flags. For example, the flag "sse4_1" comes from
@@ -148,14 +152,6 @@ needed. For instance, /proc/cpuinfo is a userspace interface and must remain
 constant. If, for some reason, the naming of X86_FEATURE_<name> changes, one
 shall override the new naming with the name already used in /proc/cpuinfo.
 
-c: The naming override can be "", which means it will not appear in /proc/cpuinfo.
-----------------------------------------------------------------------------------
-The feature shall be omitted from /proc/cpuinfo if it does not make sense for
-the feature to be exposed to userspace. For example, X86_FEATURE_ALWAYS is
-defined in cpufeatures.h but that flag is an internal kernel feature used
-in the alternative runtime patching functionality. So, its name is overridden
-with "". Its flag will not appear in /proc/cpuinfo.
-
 Flags are missing when one or more of these happen
 ==================================================
 
-- 
2.43.0

-- 
Regards/Gruss,
    Boris.

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