linux-kernel - [PATCH v3 3/7] x86: KVM: Advertise AMX-FP16 CPUID to user space

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Message-Id: <20221110015252.202566-4-jiaxi.chen@linux.intel.com>
Date:   Thu, 10 Nov 2022 09:52:48 +0800
From:   Jiaxi Chen <jiaxi.chen@...ux.intel.com>
To:     kvm@...r.kernel.org
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        seanjc@...gle.com, pbonzini@...hat.com, ndesaulniers@...gle.com,
        alexandre.belloni@...tlin.com, peterz@...radead.org,
        jpoimboe@...nel.org, chang.seok.bae@...el.com,
        pawan.kumar.gupta@...ux.intel.com, babu.moger@....com,
        jmattson@...gle.com, sandipan.das@....com, tony.luck@...el.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, fenghua.yu@...el.com,
        keescook@...omium.org, nathan@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3 3/7] x86: KVM: Advertise AMX-FP16 CPUID to user space

Latest Intel platform Granite Rapids has introduced a new instruction -
AMX-FP16, which performs dot-products of two FP16 tiles and accumulates
the results into a packed single precision tile. This instrucion needs
no additional enabling on top of the existing kernel AMX enabling.

AMX-FP16 adds FP16 capability and also allows a FP16 GPU trained model
to run faster without loss of accuracy or added SW overhead.

The bit definition:
CPUID.(EAX=7,ECX=1):EAX[bit 21]

This CPUID is exposed to user space. Besides, there is no other VMX
control for this instruction.

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

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index b388ef52f8c8..19ef02d5b11b 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_init_scattered(CPUID_7_1_EAX,
-		F(AVX_VNNI) | F(AVX512_BF16) | F(CMPCCXADD)
+		F(AVX_VNNI) | F(AVX512_BF16) | F(CMPCCXADD) | F(AMX_FP16)
 	);
 
 	kvm_cpu_cap_mask(CPUID_D_1_EAX,
diff --git a/arch/x86/kvm/reverse_cpuid.h b/arch/x86/kvm/reverse_cpuid.h
index 24f570ddb225..05fd43ebd226 100644
--- a/arch/x86/kvm/reverse_cpuid.h
+++ b/arch/x86/kvm/reverse_cpuid.h
@@ -29,6 +29,7 @@ enum kvm_only_cpuid_leafs {
 #define X86_FEATURE_AVX_VNNI            KVM_X86_FEATURE(CPUID_7_1_EAX, 4)
 #define X86_FEATURE_AVX512_BF16         KVM_X86_FEATURE(CPUID_7_1_EAX, 5)
 #define X86_FEATURE_CMPCCXADD           KVM_X86_FEATURE(CPUID_7_1_EAX, 7)
+#define X86_FEATURE_AMX_FP16            KVM_X86_FEATURE(CPUID_7_1_EAX, 21)
 
 struct cpuid_reg {
 	u32 function;
-- 
2.27.0