linux-kernel - Re: [PATCH v2 17/29] arm_mpam: Extend reset logic to allow devices to be reset any time

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Message-ID: <2c5c6e2a-e0ea-4786-ba6e-2c536a53a68b@arm.com>
Date: Thu, 2 Oct 2025 19:02:05 +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
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 17/29] arm_mpam: Extend reset logic to allow devices to
 be reset any time

Hi Ben,

On 12/09/2025 12:42, Ben Horgan wrote:
> On 9/10/25 21:42, James Morse wrote:
>> cpuhp callbacks aren't the only time the MSC configuration may need to
>> be reset. Resctrl has an API call to reset a class.
>> If an MPAM error interrupt arrives it indicates the driver has
>> misprogrammed an MSC. The safest thing to do is reset all the MSCs
>> and disable MPAM.
>>
>> Add a helper to reset RIS via their class. Call this from mpam_disable(),
>> which can be scheduled from the error interrupt handler.
>> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
>> index e7faf453b5d7..a9d3c4b09976 100644
>> --- a/drivers/resctrl/mpam_devices.c
>> +++ b/drivers/resctrl/mpam_devices.c
>> @@ -842,8 +842,6 @@ static int mpam_reset_ris(void *arg)
>>  	u16 partid, partid_max;
>>  	struct mpam_msc_ris *ris = arg;
>>
>> -	mpam_assert_srcu_read_lock_held();
>> -
>
> Remove where it is introduced. There is already one in
> mpam_reset_ris_partid() at that time.

Mmmm, this should really have been replaced with a comment.

I prefer each function to have an assert like this as documentation. In this case, a new
caller may miss the lock, but always hit the 'in_reset_state' case during testing, and be
caught out when a call to mpam_reset_ris_partid() occurs. Having documentation comments
that can also bark at you when you ignore them is really handy!

It's removed in this  patch  because calling it via mpam_touch_msc() puts it behind an
call to schedule, and lockdep expects 'current' to be the one holding the lock.

I'll add the comment. Looks like it just got dropped when mpam_touch_msc() stopped using
an IPI...


>>  	if (ris->in_reset_state)
>>  		return 0;
>
> Reviewed-by: Ben Horgan <ben.horgan@....com>

Thanks!


James