linux-kernel - Re: [RFC PATCH 02/38] arm64: mpam: Re-initialise MPAM regs when CPU comes online

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Message-ID: <b798402a-1bc4-4765-aff6-6e3c3a398987@arm.com>
Date: Thu, 11 Dec 2025 11:32:47 +0000
From: Ben Horgan <ben.horgan@....com>
To: James Morse <james.morse@....com>, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.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@...nel.org>, 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>, Gavin Shan
 <gshan@...hat.com>, rohit.mathew@....com, reinette.chatre@...el.com,
 Punit Agrawal <punit.agrawal@....qualcomm.com>
Subject: Re: [RFC PATCH 02/38] arm64: mpam: Re-initialise MPAM regs when CPU
 comes online

Retraction... sorry

On 12/11/25 11:23, Ben Horgan wrote:
> Hi James,
> 
> On 12/9/25 15:13, Ben Horgan wrote:
>> Hi James,
>>
>> On 12/5/25 21:58, James Morse wrote:

> 
> Actually, this code is only run before the mpam enablement is finished,
> importantly before the mpam_enabled static key is set, and so
> arm64_mpam_current is still 0 for every cpu. For cpus that are brought
> up after boot time this is never run.

Actually, actually, this is run whenever a cpu comes online, even if by
hotplug later, and so arm64_mpam_current will be 0 as need on the first
switch on and the previous value for the cpu when it has previously been
off.

> 
> As SYS_MPAM0_EL1 and SYS_MPAM1_EL1 are unknown out of reset we should
> set them to 0 whenever a cpu comes online to make sure they initially
> use PARTID 0 as that is the only one guaranteed to have sensible
> defaults in the MSC. Once the mpam driver has configured the MSC we can
> start setting other values.
> 
>>
>>> +
>>> +	write_sysreg_s(regval, SYS_MPAM1_EL1);
>>> +	isb();
>>> +
>>> +	write_sysreg_s(regval, SYS_MPAM0_EL1);
>>>  }
>>>  
>>>  static bool
>>
>> Thanks,
>>
>> Ben
>>
>>
> 
> Thanks,
> 
> Ben
> 
> 

-- 
Thanks,

Ben