linux-kernel - [PATCH 1/9] x86/cpufeatures: Add Slow Memory Bandwidth Allocation feature flag

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Date:   Mon, 11 Jul 2022 16:38:48 -0500
From:   Babu Moger <babu.moger@....com>
To:     <fenghua.yu@...el.com>, <reinette.chatre@...el.com>,
        <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>
CC:     <dave.hansen@...ux.intel.com>, <x86@...nel.org>, <hpa@...or.com>,
        <corbet@....net>, <hpa@...or.com>, <linux-kernel@...r.kernel.org>,
        <linux-doc@...r.kernel.org>
Subject: [PATCH 1/9] x86/cpufeatures: Add Slow Memory Bandwidth Allocation
 feature flag

Adds the new AMD feature X86_FEATURE_SMBA. With this feature, the QOS
enforcement policies can be applied to external slow memory connected
to the host. QOS enforcement is accomplished by assigning a Class Of
Service (COS) to a processor and specifying allocations or limits for
that COS for each resource to be allocated.

This feature is identified by the CPUID Function 8000_0020_EBX_x0.

CPUID Fn8000_0020_EBX_x0 AMD Bandwidth Enforcement Feature Identifiers (ECX=0)
Bits    Field Name      Description
2       L3SBE           L3 external slow memory bandwidth enforcement

Feature descriptions are available in the specification,
"AMD64 Technology Platform Quality of Service Extensions, Revision: 1.03
Publication # 56375 Revision: 1.03 Issue Date: February 2022".

Link: https://www.amd.com/en/support/tech-docs/amd64-technology-platform-quality-service-extensions
Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537

Signed-off-by: Babu Moger <babu.moger@....com>
---
 arch/x86/include/asm/cpufeatures.h |    1 +
 arch/x86/kernel/cpu/scattered.c    |    1 +
 2 files changed, 2 insertions(+)

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 03acc823838a..1db319f3ce71 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -296,6 +296,7 @@
 #define X86_FEATURE_PER_THREAD_MBA	(11*32+ 7) /* "" Per-thread Memory Bandwidth Allocation */
 #define X86_FEATURE_SGX1		(11*32+ 8) /* "" Basic SGX */
 #define X86_FEATURE_SGX2		(11*32+ 9) /* "" SGX Enclave Dynamic Memory Management (EDMM) */
+#define X86_FEATURE_SMBA		(11*32+10) /* SLOW Memory Bandwidth Allocation */
 
 /* Intel-defined CPU features, CPUID level 0x00000007:1 (EAX), word 12 */
 #define X86_FEATURE_AVX_VNNI		(12*32+ 4) /* AVX VNNI instructions */
diff --git a/arch/x86/kernel/cpu/scattered.c b/arch/x86/kernel/cpu/scattered.c
index dbaa8326d6f2..08e9c78f65e9 100644
--- a/arch/x86/kernel/cpu/scattered.c
+++ b/arch/x86/kernel/cpu/scattered.c
@@ -43,6 +43,7 @@ static const struct cpuid_bit cpuid_bits[] = {
 	{ X86_FEATURE_CPB,		CPUID_EDX,  9, 0x80000007, 0 },
 	{ X86_FEATURE_PROC_FEEDBACK,    CPUID_EDX, 11, 0x80000007, 0 },
 	{ X86_FEATURE_MBA,		CPUID_EBX,  6, 0x80000008, 0 },
+	{ X86_FEATURE_SMBA,             CPUID_EBX,  2, 0x80000020, 0 },
 	{ X86_FEATURE_PERFMON_V2,	CPUID_EAX,  0, 0x80000022, 0 },
 	{ 0, 0, 0, 0, 0 }
 };