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

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Date: Mon, 8 Apr 2024 20:23:36 -0700
From: Reinette Chatre <reinette.chatre@...el.com>
To: James Morse <james.morse@....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 James,

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?

> Signed-off-by: James Morse <james.morse@....com>
> ---

..
> diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
> index 8a7367d1ce45..6705d7960dfd 100644
> --- a/include/linux/resctrl.h
> +++ b/include/linux/resctrl.h
> @@ -200,6 +200,7 @@ struct resctrl_mon_config_info {
>  	struct rdt_domain   *d;
>  	u32                  evtid;
>  	u32                  mon_config;
> +	int                  err;
>  };

Please take care to use consistent spacing.

Reinette