linux-kernel - [PATCH] x86/cpufeatures: Add AVX512 Bit Matrix Multiply (BMM) and Bit reversal support

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Message-ID: <20260205042105.1224126-1-nikunj@amd.com>
Date: Thu, 5 Feb 2026 04:21:05 +0000
From: Nikunj A Dadhania <nikunj@....com>
To: <seanjc@...gle.com>, <pbonzini@...hat.com>, <bp@...en8.de>
CC: <x86@...nel.org>, <babu.moger@....com>, <linux-kernel@...r.kernel.org>,
	<kvm@...r.kernel.org>, <thomas.lendacky@....com>, <santosh.shukla@....com>,
	<nikunj@....com>
Subject: [PATCH] x86/cpufeatures: Add AVX512 Bit Matrix Multiply (BMM) and Bit reversal support

Add support for AVX512 Bit Matrix Multiply (BMM) and Bit Reversal
instructions, a feature that enables bit matrix multiply operations and
bit reversal, which is exposed via CPUID leaf 0x80000021_EAX[23].

Expose the support to guests when available by including it in the CPUID
leaf 0x80000021_EAX feature list.

While at it, reorder PREFETCHI to match the bit position order in CPUID
leaf 0x80000021_EAX for better organization.

Signed-off-by: Nikunj A Dadhania <nikunj@....com>
---

AMD64 Bit Matrix Multiply and Bit Reversal Instructions
Publication #69192 Revision: 1.00
Issue Date: January 2026

https://docs.amd.com/v/u/en-US/69192-PUB
---
 arch/x86/include/asm/cpufeatures.h | 1 +
 arch/x86/kvm/cpuid.c               | 3 ++-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index c3b53beb1300..2f1583c4bdc0 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -472,6 +472,7 @@
 #define X86_FEATURE_GP_ON_USER_CPUID	(20*32+17) /* User CPUID faulting */
 
 #define X86_FEATURE_PREFETCHI		(20*32+20) /* Prefetch Data/Instruction to Cache Level */
+#define X86_FEATURE_AVX512_BMM		(20*32+23) /* AVX512 Bit Matrix Multiply instructions */
 #define X86_FEATURE_SBPB		(20*32+27) /* Selective Branch Prediction Barrier */
 #define X86_FEATURE_IBPB_BRTYPE		(20*32+28) /* MSR_PRED_CMD[IBPB] flushes all branch type predictions */
 #define X86_FEATURE_SRSO_NO		(20*32+29) /* CPU is not affected by SRSO */
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 88a5426674a1..b36e8f10f509 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -1218,11 +1218,12 @@ void kvm_set_cpu_caps(void)
 		F(NULL_SEL_CLR_BASE),
 		/* UpperAddressIgnore */
 		F(AUTOIBRS),
-		F(PREFETCHI),
 		EMULATED_F(NO_SMM_CTL_MSR),
 		/* PrefetchCtlMsr */
 		/* GpOnUserCpuid */
 		/* EPSF */
+		F(PREFETCHI),
+		F(AVX512_BMM),
 		SYNTHESIZED_F(SBPB),
 		SYNTHESIZED_F(IBPB_BRTYPE),
 		SYNTHESIZED_F(SRSO_NO),

base-commit: e89f0e9a0a007e8c3afb8ecd739c0b3255422b00
-- 
2.48.1