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Message-ID: <af829bf9-28b2-4b3d-9252-075201689052@arm.com>
Date: Fri, 14 Jun 2024 14:57:52 +0100
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Subject: Re: [PATCH v1 18/31] x86/resctrl: Allow
 resctrl_arch_mon_event_config_write() to return an error
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To: Reinette Chatre <reinette.chatre@intel.com>, x86@kernel.org,
 linux-kernel@vger.kernel.org
Cc: Fenghua Yu <fenghua.yu@intel.com>, Thomas Gleixner <tglx@linutronix.de>,
 Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
 H Peter Anvin <hpa@zytor.com>, Babu Moger <Babu.Moger@amd.com>,
 shameerali.kolothum.thodi@huawei.com,
 D Scott Phillips OS <scott@os.amperecomputing.com>,
 carl@os.amperecomputing.com, lcherian@marvell.com,
 bobo.shaobowang@huawei.com, tan.shaopeng@fujitsu.com,
 baolin.wang@linux.alibaba.com, Jamie Iles <quic_jiles@quicinc.com>,
 Xin Hao <xhao@linux.alibaba.com>, peternewman@google.com,
 dfustini@baylibre.com, amitsinght@marvell.com,
 David Hildenbrand <david@redhat.com>, Rex Nie <rex.nie@jaguarmicro.com>,
 Dave Martin <dave.martin@arm.com>
References: <20240321165106.31602-1-james.morse@arm.com>
 <20240321165106.31602-19-james.morse@arm.com>
 <d598767d-1c44-4417-9dc6-7078c97df39f@intel.com>
From: James Morse <james.morse@arm.com>
In-Reply-To: <d598767d-1c44-4417-9dc6-7078c97df39f@intel.com>
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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