[PATCH 1/6] x86: KVM: Enable CMPccXADD CPUID and expose it to guest

Jiaxi Chen
2022-10-19T08:57:08Z

CMPccXADD is a new set of instructions in the latest Intel platform Sierra
Forest. It includes a semaphore operation that can compare and add the
operands if condition is met, which can improve database performance.

The bit definition:
CPUID.(EAX=7,ECX=1):EAX[bit 7]

This patch enables this CPUID in the kernel feature bits and expose it to
guest OS.

Signed-off-by: Jiaxi Chen <jiaxi.chen@linux.intel.com>
---
arch/x86/include/asm/cpufeatures.h | 1 +
arch/x86/kvm/cpuid.c | 2 +-
2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index ef4775c6db01..445626cb5779 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -308,6 +308,7 @@
/* Intel-defined CPU features, CPUID level 0x00000007:1 (EAX), word 12 */
#define X86_FEATURE_AVX_VNNI (12*32+ 4) /* AVX VNNI instructions */
#define X86_FEATURE_AVX512_BF16 (12*32+ 5) /* AVX512 BFLOAT16 instructions */
+#define X86_FEATURE_CMPCCXADD (12*32+ 7) /* CMPccXADD instructions */

/* AMD-defined CPU features, CPUID level 0x80000008 (EBX), word 13 */
#define X86_FEATURE_CLZERO (13*32+ 0) /* CLZERO instruction */
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 7065462378e2..3f745f6fdc43 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -657,7 +657,7 @@ void kvm_set_cpu_caps(void)
kvm_cpu_cap_set(X86_FEATURE_SPEC_CTRL_SSBD);

kvm_cpu_cap_mask(CPUID_7_1_EAX,
- F(AVX_VNNI) | F(AVX512_BF16)
+ F(AVX_VNNI) | F(AVX512_BF16) | F(CMPCCXADD)
);

kvm_cpu_cap_mask(CPUID_D_1_EAX,
--
2.27.0