linux-kernel - Re: [PATCH v1 18/31] x86/resctrl: Allow resctrl_arch_mon_event_config

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Date: Fri, 14 Jun 2024 14:57:52 +0100
From: James Morse <james.morse@....com>
To: Reinette Chatre <reinette.chatre@...el.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Cc: Fenghua Yu <fenghua.yu@...el.com>, Thomas Gleixner <tglx@...utronix.de>,
 Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
 H Peter Anvin <hpa@...or.com>, Babu Moger <Babu.Moger@....com>,
 shameerali.kolothum.thodi@...wei.com,
 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>, Rex Nie <rex.nie@...uarmicro.com>,
 Dave Martin <dave.martin@....com>
Subject: Re: [PATCH v1 18/31] x86/resctrl: Allow
 resctrl_arch_mon_event_config_write() to return an error

Hi Reinette,

On 09/04/2024 04:23, Reinette Chatre wrote:
> On 3/21/2024 9:50 AM, James Morse wrote:
>> resctrl_arch_mon_event_config_write() writes a bitmap of events provided
>> by user-space into the configuration register for the monitors.
>>
>> This assumes that all architectures support all the features each bit
>> corresponds to.
>>
>> MPAM can filter monitors based on read, write, or both, but there are
>> many more options in the existing bitmap. To allow this interface to
>> work for machines with MPAM, allow the architecture helper to return
>> an error if an incompatible bitmap is set.
>>
>> When valid values are provided, there is no change in behaviour. If
>> an invalid value is provided, currently it is silently ignored, but
>> last_cmd_status is updated. After this change, the parser will stop
>> at the first invalid value and return an error to user-space. This
>> matches the way changes to the schemata file are made.
>>
> 
> Is this needed? With move of mbm_cfg_mask to rdt_resource I expect
> MPAM would use it to set what the valid values are. With that done,
> when user space provides a value, mon_config_write() compares user
> provided value against mbm_cfg_mask and will already return early
> (before attempting to write to hardware) with error
> if value is not supported. This seems to accomplish the goal of this
> patch?

Aha, this is done in mon_config_write(), not mbm_config_write_domain(). I'd missed that.
I'll drop this patch.

Thanks!

James