linux-kernel - Re: [PATCH v4 05/41] arm64: mpam: Re-initialise MPAM regs when CPU comes online

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Message-ID: <aYTDUStE3RJp_ht4@arm.com>
Date: Thu, 5 Feb 2026 16:20:33 +0000
From: Catalin Marinas <catalin.marinas@....com>
To: Ben Horgan <ben.horgan@....com>
Cc: amitsinght@...vell.com, baisheng.gao@...soc.com,
	baolin.wang@...ux.alibaba.com, carl@...amperecomputing.com,
	dave.martin@....com, david@...nel.org, dfustini@...libre.com,
	fenghuay@...dia.com, gshan@...hat.com, james.morse@....com,
	jonathan.cameron@...wei.com, kobak@...dia.com, lcherian@...vell.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
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	rohit.mathew@....com, scott@...amperecomputing.com,
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	zengheng4@...wei.com, linux-doc@...r.kernel.org,
	Shaopeng Tan <tan.shaopeng@...fujitsu.com>
Subject: Re: [PATCH v4 05/41] arm64: mpam: Re-initialise MPAM regs when CPU
 comes online

On Tue, Feb 03, 2026 at 09:43:06PM +0000, Ben Horgan wrote:
> From: James Morse <james.morse@....com>
> 
> Now that the MPAM system registers are expected to have values that change,
> reprogram them based on the previous value when a CPU is brought online.
> 
> Previously MPAM's 'default PARTID' of 0 was always used for MPAM in
> kernel-space as this is the PARTID that hardware guarantees to
> reset. Because there are a limited number of PARTID, this value is exposed
> to user-space, meaning resctrl changes to the resctrl default group would
> also affect kernel threads.  Instead, use the task's PARTID value for
> kernel work on behalf of user-space too. The default of 0 is kept for both
> user-space and kernel-space when MPAM is not enabled.
> 
> Tested-by: Gavin Shan <gshan@...hat.com>
> Tested-by: Shaopeng Tan <tan.shaopeng@...fujitsu.com>
> Tested-by: Peter Newman <peternewman@...gle.com>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@...wei.com>
> Signed-off-by: James Morse <james.morse@....com>
> Reviewed-by: Gavin Shan <gshan@...hat.com>
> Signed-off-by: Ben Horgan <ben.horgan@....com>

Reviewed-by: Catalin Marinas <catalin.marinas@....com>