linux-kernel - [PATCH v2 02/10] x86/cpufeatures: Add Slow Memory Bandwidth Allocation feature flag

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Date:   Mon, 1 Aug 2022 15:55:53 -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:     <eranian@...gle.com>, <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 v2 02/10] 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 description is 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 a77b915d36a8..14b5cc8da75c 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -303,6 +303,7 @@
 #define X86_FEATURE_RETHUNK		(11*32+14) /* "" Use REturn THUNK */
 #define X86_FEATURE_UNRET		(11*32+15) /* "" AMD BTB untrain return */
 #define X86_FEATURE_USE_IBPB_FW		(11*32+16) /* "" Use IBPB during runtime firmware calls */
+#define X86_FEATURE_SMBA		(11*32+17) /* 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 fd44b54c90d5..885ecf46abb2 100644
--- a/arch/x86/kernel/cpu/scattered.c
+++ b/arch/x86/kernel/cpu/scattered.c
@@ -44,6 +44,7 @@ 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 }
 };