linux-kernel - Re: [PATCH v2 15/29] arm_mpam: Reset MSC controls from cpu hp callbacks

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Message-ID: <52b6bd30-55af-4916-89c0-f87446689fbe@arm.com>
Date: Fri, 12 Sep 2025 15:52:03 +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 15/29] arm_mpam: Reset MSC controls from cpu hp
 callbacks



On 9/12/25 12:25, Ben Horgan wrote:
> Hi James,
> 
> On 9/10/25 21:42, James Morse wrote:
>> When a CPU comes online, it may bring a newly accessible MSC with
>> it. Only the default partid has its value reset by hardware, and
>> even then the MSC might not have been reset since its config was
>> previously dirtyied. e.g. Kexec.
>>
>> Any in-use partid must have its configuration restored, or reset.
>> In-use partids may be held in caches and evicted later.
>>
>> MSC are also reset when CPUs are taken offline to cover cases where
>> firmware doesn't reset the MSC over reboot using UEFI, or kexec
>> where there is no firmware involvement.
>>
>> If the configuration for a RIS has not been touched since it was
>> brought online, it does not need resetting again.
>>
>> To reset, write the maximum values for all discovered controls.
>>
>> CC: Rohit Mathew <Rohit.Mathew@....com>
>> Signed-off-by: James Morse <james.morse@....com>
>> ---
>> Changes since RFC:
>>  * Last bitmap write will always be non-zero.
>>  * Dropped READ_ONCE() - teh value can no longer change.
>>  * Write 0 to proporitional stride, remove the bwa_fract variable.
>>  * Removed nested srcu lock, the assert should cover it.
>> ---
>>  drivers/resctrl/mpam_devices.c  | 117 ++++++++++++++++++++++++++++++++
>>  drivers/resctrl/mpam_internal.h |   8 +++
>>  2 files changed, 125 insertions(+)
>>
>> +
>> +static void mpam_reset_msc(struct mpam_msc *msc, bool online)
>> +{
>> +	struct mpam_msc_ris *ris;
>> +
>> +	mpam_assert_srcu_read_lock_held();
> 
> Unneeded? Checked in list_for_each_entry_srcu().> +

If you do get rid of this then that leaves one use of the helper,
mpam_assert_srcu_read_lock_held(), and so the helper could go.

> Thanks,
> 
> Ben
> 
> 

Thanks,

Ben