linux-kernel - Re: [PATCH 07/33] arm64: kconfig: Add Kconfig entry for MPAM

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Message-ID: <fb8731ac-49ef-4a1a-91f2-daa1531c9ea7@arm.com>
Date: Thu, 28 Aug 2025 16:58:26 +0100
From: James Morse <james.morse@....com>
To: Ben Horgan <ben.horgan@....com>, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org,
 devicetree@...r.kernel.org
Cc: shameerali.kolothum.thodi@...wei.com,
 D Scott Phillips OS <scott@...amperecomputing.com>,
 carl@...amperecomputing.com, lcherian@...vell.com,
 bobo.shaobowang@...wei.com, tan.shaopeng@...itsu.com,
 baolin.wang@...ux.alibaba.com, Jamie Iles <quic_jiles@...cinc.com>,
 Xin Hao <xhao@...ux.alibaba.com>, peternewman@...gle.com,
 dfustini@...libre.com, amitsinght@...vell.com,
 David Hildenbrand <david@...hat.com>, Rex Nie <rex.nie@...uarmicro.com>,
 Dave Martin <dave.martin@....com>, Koba Ko <kobak@...dia.com>,
 Shanker Donthineni <sdonthineni@...dia.com>, fenghuay@...dia.com,
 baisheng.gao@...soc.com, Jonathan Cameron <jonathan.cameron@...wei.com>,
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 <guohanjun@...wei.com>, Sudeep Holla <sudeep.holla@....com>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Catalin Marinas <catalin.marinas@....com>,
 Will Deacon <will@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Danilo Krummrich <dakr@...nel.org>
Subject: Re: [PATCH 07/33] arm64: kconfig: Add Kconfig entry for MPAM

Hi Ben,

On 27/08/2025 09:53, Ben Horgan wrote:
> On 8/22/25 16:29, James Morse wrote:
>> The bulk of the MPAM driver lives outside the arch code because it
>> largely manages MMIO devices that generate interrupts. The driver
>> needs a Kconfig symbol to enable it, as MPAM is only found on arm64
>> platforms, that is where the Kconfig option makes the most sense.
>>
>> This Kconfig option will later be used by the arch code to enable
>> or disable the MPAM context-switch code, and registering the CPUs
>> properties with the MPAM driver.

>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>> index e9bbfacc35a6..658e47fc0c5a 100644
>> --- a/arch/arm64/Kconfig
>> +++ b/arch/arm64/Kconfig
>> @@ -2060,6 +2060,23 @@ config ARM64_TLB_RANGE
>>  	  ARMv8.4-TLBI provides TLBI invalidation instruction that apply to a
>>  	  range of input addresses.
>>  
>> +config ARM64_MPAM
>> +	bool "Enable support for MPAM"
>> +	help
>> +	  Memory Partitioning and Monitoring is an optional extension
>> +	  that allows the CPUs to mark load and store transactions with
>> +	  labels for partition-id and performance-monitoring-group.
>> +	  System components, such as the caches, can use the partition-id
>> +	  to apply a performance policy. MPAM monitors can use the
>> +	  partition-id and performance-monitoring-group to measure the
>> +	  cache occupancy or data throughput.
>> +
>> +	  Use of this extension requires CPU support, support in the
>> +	  memory system components (MSC), and a description from firmware
>> +	  of where the MSC are in the address space.
>> +
>> +	  MPAM is exposed to user-space via the resctrl pseudo filesystem.
>> +
>>  endmenu # "ARMv8.4 architectural features"

> Should this be moved to "ARMv8.2 architectural features" rather than the
> 8.4 menu? In the arm reference manual, version L.b, I see FEAT_MPAM
> listed in the section A2.2.3.1 Features added to the Armv8.2 extension
> in later releases.

Hmmm, I don't think we've done that anywhere else. I'm only aware of one v8.2 platform
that had it, and those are not widely available. As it was a headline v8.4 feature I'd
prefer to keep it there.

I think its more confusing to put it under v8.2!


Thanks,

James