KVM: x86: Advertise AVX10_VNNI_INT CPUID to userspace

Define and advertise AVX10_VNNI_INT CPUID to userspace when it's supported
by the host.

AVX10_VNNI_INT (0x24.0x1.ECX[bit 2]) is a discrete feature bit
introduced on Intel Diamond Rapids, which enumerates the support for
EVEX VPDP* instructions for INT8/INT16 [*].

Since this feature has no actual kernel usages, define it as a KVM-only
feature in reverse_cpuid.h.

Advertise new CPUID subleaf 0x24.0x1 with AVX10_VNNI_INT bit to
userspace for guest use. It's safe since no additional enabling work
is needed in the host kernel.

[*]: Intel Advanced Vector Extensions 10.2 Architecture Specification
     (rev 5.0).

Tested-by: Xudong Hao <xudong.hao@intel.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Link: https://patch.msgid.link/20251120050720.931449-5-zhao1.liu@intel.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

Author: trueptolemy

arch/x86/include/asm/kvm_host.h

@@ -777,6 +777,7 @@ enum kvm_only_cpuid_leafs {
 	CPUID_8000_0021_ECX,
 	CPUID_7_1_ECX,
 	CPUID_1E_1_EAX,
+	CPUID_24_1_ECX,
 	NR_KVM_CPU_CAPS,
 
 	NKVMCAPINTS = NR_KVM_CPU_CAPS - NCAPINTS,

arch/x86/kvm/cpuid.c

@@ -1084,6 +1084,10 @@ void kvm_set_cpu_caps(void)
 		F(AVX10_512),
 	);
 
+	kvm_cpu_cap_init(CPUID_24_1_ECX,
+		F(AVX10_VNNI_INT),
+	);
+
 	kvm_cpu_cap_init(CPUID_8000_0001_ECX,
 		F(LAHF_LM),
 		F(CMP_LEGACY),
@@ -1661,6 +1665,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 			break;
 		}
 
+		max_idx = entry->eax = min(entry->eax, 1u);
 		/*
 		 * The AVX10 version is encoded in EBX[7:0].  Note, the version
 		 * is guaranteed to be >=1 if AVX10 is supported.  Note #2, the
@@ -1670,9 +1675,20 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 		cpuid_entry_override(entry, CPUID_24_0_EBX);
 		entry->ebx |= avx10_version;
 
-		entry->eax = 0;
 		entry->ecx = 0;
 		entry->edx = 0;
+
+		/* KVM only supports up to 0x24.0x1, capped above via min(). */
+		if (max_idx >= 1) {
+			entry = do_host_cpuid(array, function, 1);
+			if (!entry)
+				goto out;
+
+			cpuid_entry_override(entry, CPUID_24_1_ECX);
+			entry->eax = 0;
+			entry->ebx = 0;
+			entry->edx = 0;
+		}
 		break;
 	}
 	case KVM_CPUID_SIGNATURE: {

arch/x86/kvm/reverse_cpuid.h

@@ -63,6 +63,9 @@
 #define X86_FEATURE_AVX10_256		KVM_X86_FEATURE(CPUID_24_0_EBX, 17)
 #define X86_FEATURE_AVX10_512		KVM_X86_FEATURE(CPUID_24_0_EBX, 18)
 
+/* Intel-defined sub-features, CPUID level 0x00000024:1 (ECX) */
+#define X86_FEATURE_AVX10_VNNI_INT	KVM_X86_FEATURE(CPUID_24_1_ECX, 2)
+
 /* CPUID level 0x80000007 (EDX). */
 #define KVM_X86_FEATURE_CONSTANT_TSC	KVM_X86_FEATURE(CPUID_8000_0007_EDX, 8)
 
@@ -105,6 +108,7 @@ static const struct cpuid_reg reverse_cpuid[] = {
 	[CPUID_8000_0021_ECX] = {0x80000021, 0, CPUID_ECX},
 	[CPUID_7_1_ECX]       = {         7, 1, CPUID_ECX},
 	[CPUID_1E_1_EAX]      = {      0x1e, 1, CPUID_EAX},
+	[CPUID_24_1_ECX]      = {      0x24, 1, CPUID_ECX},
 };
 
 /*