[PATCH v1 1/3] x86/cpufeatures: Add low performance CRC32C instruction CPU feature

[Tony W Wang-oc]

SSE4.2 on Zhaoxin CPUs are compatible with Intel. The presence of
CRC32C instruction is enumerated by CPUID.01H:ECX.SSE4_2[bit 20] = 1.
Some Zhaoxin CPUs declare support SSE4.2 instruction sets but their
CRC32C instruction are working with low performance.

Add a synthetic CPU flag to indicates that the CRC32C instruction is
not working as intended. This low performance CRC32C instruction flag
is depend on X86_FEATURE_XMM4_2.

Signed-off-by: Tony W Wang-oc <TonyWWang-oc@xxxxxxxxxxx>
---
 arch/x86/include/asm/cpufeatures.h | 1 +
 arch/x86/kernel/cpu/cpuid-deps.c   | 1 +
 2 files changed, 2 insertions(+)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 84b8878..9e8151b 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -292,6 +292,7 @@
 #define X86_FEATURE_FENCE_SWAPGS_KERNEL	(11*32+ 5) /* "" LFENCE in kernel entry SWAPGS path */
 #define X86_FEATURE_SPLIT_LOCK_DETECT	(11*32+ 6) /* #AC for split lock */
 #define X86_FEATURE_PER_THREAD_MBA	(11*32+ 7) /* "" Per-thread Memory Bandwidth Allocation */
+#define X86_FEATURE_CRC32C		(11*32+ 8) /* "" Low performance CRC32C instruction */
 
 /* Intel-defined CPU features, CPUID level 0x00000007:1 (EAX), word 12 */
 #define X86_FEATURE_AVX512_BF16		(12*32+ 5) /* AVX512 BFLOAT16 instructions */
diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-deps.c
index 42af31b6..7d7fca7 100644
--- a/arch/x86/kernel/cpu/cpuid-deps.c
+++ b/arch/x86/kernel/cpu/cpuid-deps.c
@@ -72,6 +72,7 @@ static const struct cpuid_dep cpuid_deps[] = {
 	{ X86_FEATURE_AVX512_FP16,		X86_FEATURE_AVX512BW  },
 	{ X86_FEATURE_ENQCMD,			X86_FEATURE_XSAVES    },
 	{ X86_FEATURE_PER_THREAD_MBA,		X86_FEATURE_MBA       },
+	{ X86_FEATURE_CRC32C,			X86_FEATURE_XMM4_2    },
 	{}
 };
 
-- 
2.7.4