x86/cpufeatures: Add feature bit RDPRU on AMD

AMD Zen 2 introduces a new RDPRU instruction which is used to give
access to some processor registers that are typically only accessible
when the privilege level is zero.

ECX is used as the implicit register to specify which register to read.
RDPRU places the specified register’s value into EDX:EAX.

For example, the RDPRU instruction can be used to read MPERF and APERF
at CPL > 0.

Add the feature bit so it is visible in /proc/cpuinfo.

Details are available in the AMD64 Architecture Programmer’s Manual:
https://www.amd.com/system/files/TechDocs/24594.pdf

Signed-off-by: Babu Moger <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Cc: Aaron Lewis <[email protected]>
Cc: [email protected]
Cc: Fenghua Yu <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Cc: "Peter Zijlstra (Intel)" <[email protected]>
Cc: [email protected]
Cc: Thomas Gleixner <[email protected]>
Cc: Thomas Hellstrom <[email protected]>
Cc: x86-ml <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

Author: babumoger

arch/x86/include/asm/cpufeatures.h

@@ -292,6 +292,7 @@
 #define X86_FEATURE_CLZERO		(13*32+ 0) /* CLZERO instruction */
 #define X86_FEATURE_IRPERF		(13*32+ 1) /* Instructions Retired Count */
 #define X86_FEATURE_XSAVEERPTR		(13*32+ 2) /* Always save/restore FP error pointers */
+#define X86_FEATURE_RDPRU		(13*32+ 4) /* Read processor register at user level */
 #define X86_FEATURE_WBNOINVD		(13*32+ 9) /* WBNOINVD instruction */
 #define X86_FEATURE_AMD_IBPB		(13*32+12) /* "" Indirect Branch Prediction Barrier */
 #define X86_FEATURE_AMD_IBRS		(13*32+14) /* "" Indirect Branch Restricted Speculation */