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

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Date:   Thu, 7 Jan 2021 14:19:06 +0800
From:   Tony W Wang-oc <TonyWWang-oc@...oxin.com>
To:     <herbert@...dor.apana.org.au>, <davem@...emloft.net>,
        <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
        <x86@...nel.org>, <hpa@...or.com>, <tony.luck@...el.com>,
        <dave.hansen@...el.com>, <seanjc@...gle.com>,
        <fenghua.yu@...el.com>, <thomas.lendacky@....com>,
        <kyung.min.park@...el.com>, <kim.phillips@....com>,
        <mgross@...ux.intel.com>, <peterz@...radead.org>,
        <krish.sadhukhan@...cle.com>, <liam.merwick@...cle.com>,
        <mlevitsk@...hat.com>, <reinette.chatre@...el.com>,
        <babu.moger@....com>, <linux-crypto@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC:     <TimGuo-oc@...oxin.com>, <CooperYan@...oxin.com>,
        <QiyuanWang@...oxin.com>, <HerryYang@...oxin.com>,
        <CobeChen@...oxin.com>, <SilviaZhao@...oxin.com>
Subject: [PATCH v1 1/3] x86/cpufeatures: Add low performance CRC32C instruction CPU feature

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@...oxin.com>
---
 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