linux-kernel - Re: [PATCH v2 05/29] arm64: kconfig: Add Kconfig entry for MPAM

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Message-ID: <3a93f4f3-cafc-40f5-b405-d42d5f5c9525@arm.com>
Date: Fri, 12 Sep 2025 11:14:59 +0100
From: Ben Horgan <ben.horgan@....com>
To: James Morse <james.morse@....com>, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org
Cc: 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>, 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>, Rob Herring
 <robh@...nel.org>, Rohit Mathew <rohit.mathew@....com>,
 Rafael Wysocki <rafael@...nel.org>, Len Brown <lenb@...nel.org>,
 Lorenzo Pieralisi <lpieralisi@...nel.org>, Hanjun Guo
 <guohanjun@...wei.com>, Sudeep Holla <sudeep.holla@....com>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Danilo Krummrich <dakr@...nel.org>
Subject: Re: [PATCH v2 05/29] arm64: kconfig: Add Kconfig entry for MPAM

Hi James,

On 9/10/25 21:42, 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, the arm64 tree is the most natural home for the Kconfig
> option.
> 
> This Kconfig option will later be used by the arch code to enable
> or disable the MPAM context-switch code, and to register properties
> of CPUs with the MPAM driver.
> 
> Signed-off-by: James Morse <james.morse@....com>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>
> CC: Dave Martin <dave.martin@....com>
> ---
> Changes since v1:
>  * Help text rewritten by Dave.
> ---
>  arch/arm64/Kconfig | 23 +++++++++++++++++++++++
>  1 file changed, 23 insertions(+)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index e9bbfacc35a6..4be8a13505bf 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -2060,6 +2060,29 @@ 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 System Resource Partitioning and Monitoring (MPAM) is an
> +	  optional extension to the Arm architecture that allows each
> +	  transaction issued to the memory system to be labelled with a
> +	  Partition identifier (PARTID) and Performance Monitoring Group
> +	  identifier (PMG).
> +
> +	  Memory system components, such as the caches, can be configured with
> +	  policies to control how much of various physical resources (such as
> +	  memory bandwidth or cache memory) the transactions labelled with each
> +	  PARTID can consume.  Depending on the capabilities of the hardware,
> +	  the PARTID and PMG can also be used as filtering criteria to measure
> +	  the memory system resource consumption of different parts of a
> +	  workload.
> +
> +	  Use of this extension requires CPU support, support in the
> +	  Memory System Components (MSC), and a description from firmware
> +	  of where the MSCs are in the address space.
> +
> +	  MPAM is exposed to user-space via the resctrl pseudo filesystem.
> +
>  endmenu # "ARMv8.4 architectural features"
>  
>  menu "ARMv8.5 architectural features"

Seems good to me. I guess we can consider separately whether we want
this to be default or not.

Reviewed-by: Ben Horgan <ben.horgan@....com>

Thanks,

Ben