linux-kernel - [PATCH RFC v1 19/20] KVM: x86: Expose APX sub-features to guests

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Message-ID: <20251110180131.28264-20-chang.seok.bae@intel.com>
Date: Mon, 10 Nov 2025 18:01:30 +0000
From: "Chang S. Bae" <chang.seok.bae@...el.com>
To: kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: pbonzini@...hat.com,
	seanjc@...gle.com,
	chao.gao@...el.com,
	zhao1.liu@...el.com,
	chang.seok.bae@...el.com
Subject: [PATCH RFC v1 19/20] KVM: x86: Expose APX sub-features to guests

Add CPUID leaf 0x29 sub-leaf 0 to enumerate APX sub-features to guests.
This leaf currently defines the following sub-features:

  * New Conditional Instructions (NCI)
  * New Data Destination (NDD)
  * Flags Suppression (NF)

The CPUID leaf is only exposed if the APX feature is enabled.

Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com>
---
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/cpuid.c            | 10 ++++++++--
 arch/x86/kvm/reverse_cpuid.h    |  4 ++++
 3 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 940f83c121cf..763872080c64 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -794,6 +794,7 @@ enum kvm_only_cpuid_leafs {
 	CPUID_24_0_EBX,
 	CPUID_8000_0021_ECX,
 	CPUID_7_1_ECX,
+	CPUID_29_0_EBX,
 	NR_KVM_CPU_CAPS,
 
 	NKVMCAPINTS = NR_KVM_CPU_CAPS - NCAPINTS,
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index b90e58f2a42f..95c25de641ca 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -1063,6 +1063,10 @@ void kvm_set_cpu_caps(void)
 		F(AVX10_512),
 	);
 
+	kvm_cpu_cap_init(CPUID_29_0_EBX,
+		F(APX_NCI_NDD_NF),
+	);
+
 	kvm_cpu_cap_init(CPUID_8000_0001_ECX,
 		F(LAHF_LM),
 		F(CMP_LEGACY),
@@ -1640,8 +1644,10 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 		break;
 	}
 	case 0x29: {
-		/* No APX sub-features are supported yet */
-		entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
+		if (!(kvm_caps.supported_xcr0 & XFEATURE_MASK_APX)) {
+			entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
+			break;
+		}
 		break;
 	}
 	case KVM_CPUID_SIGNATURE: {
diff --git a/arch/x86/kvm/reverse_cpuid.h b/arch/x86/kvm/reverse_cpuid.h
index e9d9fb4070ca..a8eca23ee2d4 100644
--- a/arch/x86/kvm/reverse_cpuid.h
+++ b/arch/x86/kvm/reverse_cpuid.h
@@ -50,6 +50,9 @@
 #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 0x00000029:0 (EBX) */
+#define X86_FEATURE_APX_NCI_NDD_NF	KVM_X86_FEATURE(CPUID_29_0_EBX, 0)
+
 /* CPUID level 0x80000007 (EDX). */
 #define KVM_X86_FEATURE_CONSTANT_TSC	KVM_X86_FEATURE(CPUID_8000_0007_EDX, 8)
 
@@ -92,6 +95,7 @@ static const struct cpuid_reg reverse_cpuid[] = {
 	[CPUID_24_0_EBX]      = {      0x24, 0, CPUID_EBX},
 	[CPUID_8000_0021_ECX] = {0x80000021, 0, CPUID_ECX},
 	[CPUID_7_1_ECX]       = {         7, 1, CPUID_ECX},
+	[CPUID_29_0_EBX]      = {      0x29, 0, CPUID_EBX},
 };
 
 /*
-- 
2.51.0