Received-SPF: pass (google.com: domain of linux-kernel+bounces-141416-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.48.161 as permitted sender) client-ip=147.75.48.161;
Message-ID: <fbb116ab-d3db-4ab0-a597-980f85866db9@intel.com>
Date: Thu, 11 Apr 2024 10:39:37 -0700
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH v1 18/31] x86/resctrl: Allow
 resctrl_arch_mon_event_config_write() to return an error
To: Dave Martin <Dave.Martin@arm.com>
CC: James Morse <james.morse@arm.com>, <x86@kernel.org>,
	<linux-kernel@vger.kernel.org>, 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>
References: <20240321165106.31602-1-james.morse@arm.com>
 <20240321165106.31602-19-james.morse@arm.com>
 <d598767d-1c44-4417-9dc6-7078c97df39f@intel.com>
 <Zhfw3d3YCKu7PD3G@e133380.arm.com>
Content-Language: en-US
From: Reinette Chatre <reinette.chatre@intel.com>
In-Reply-To: <Zhfw3d3YCKu7PD3G@e133380.arm.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
Precedence: bulk
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?bXFqWGFEdUZkNmEwa2hGRENqWWY4aUxId3IvNjNYQ2R5dk5vcWFJQXZHeEdD?=
 =?utf-8?B?QkQzdVp0UWNOS21qRUZHRWZrZldaM1hKaUdwWWprdStDcEtuZVExS0VTL1hL?=
 =?utf-8?B?TjlSSSt5eU1wSy9oUkRTOEc0SnRCNVNadU9BWExOczVIMndyZ2c4blZRcjd4?=
 =?utf-8?B?L3J3cUhWZmVZSHJnR2prRm5EdEdjUUt5QjRER3FncDlFZmhab2o4TXp1TnZO?=
 =?utf-8?B?bktpYkdtSzdQQ1hoRmZFOXkzQmhwM2QwV2RZNnV0bXRQOEwrRk9BTHdCUFV4?=
 =?utf-8?B?SGgzWHFLQzZWOUhhSzczRk52RTArT0RmZmd4Y2daYWE5MjZlRllNdmdiNlBL?=
 =?utf-8?B?WCtLLzM2WnZtd3lsakZYVVRaME0vOHQ3a2pGbHpUeEFHZndqZlFxZVFxMUI5?=
 =?utf-8?B?VzRYcjkvQlQ4alAvaGlNSlFWSU1uWVpleERpalNwWUNmNEdIZC9oeXFOdThu?=
 =?utf-8?B?cTRUVTFSWG9wTVA0OG9WY1hDNW82ODZhSFVCV1NzMUFlZkFXV3oyMy9OdGQr?=
 =?utf-8?B?SkUxMWpNb0JWenY3MkQwbnBIczlQVzlCR1ZsWnJFZmZvMVNzMmlPZ1lqYURu?=
 =?utf-8?B?dTZCSXQrRVRUZmlaNHFuT092R0ZvWGxHZTJyeHNjbS9ZS0ZHWjE3ZllCcHo1?=
 =?utf-8?B?dDJGYitERHFmN0xrYWR1UERjODJ4ZU5ENVcyU0hreDlFYWJZRU5lMjVjcUtl?=
 =?utf-8?B?Z2hSVEdRcFh5bDY4RmdhbGJDcmoxRWp6WXBSRjVpWVMxTlhDMzI5Z0lPTWdE?=
 =?utf-8?B?ZTg4b2NoV0dxQ0x1bGNjNWRyM09XOURRczh0eU9iVFJTRmJmQ1NkcHdaTFF3?=
 =?utf-8?B?QWlVK1AyajltUmw0QVVHaE5sc1prTWhjYVVLSVg1WGl0TTJvczZsUklVeXVO?=
 =?utf-8?B?c280WFRqSHVNdEFWUEN0UTRFeEhVVFpFbHdwdC83R0hNNjJPWi8yeGxNRi90?=
 =?utf-8?B?Q2Z0VW9vciswSDZUQWJhaWZETHBoaWxjVDQxSk1JWlBoRVYwdHJ1NC90eTdx?=
 =?utf-8?B?NlhqSHgxSUlRSGhrdmhBdllrZStvb01SRUlSTVFaWlJsYjV1WmhER2FLbFYz?=
 =?utf-8?B?bmdjY2lZUlZ4aldOQWRQQVpVVmhoTDRyRjRQZGJKZGd5RTdXcWJmZkhsakJC?=
 =?utf-8?B?anRGSUdNU1hUa1JpRnRlYitkWks3c251U1hjam9iQ0xWbjZUSHRRcXVyMmJM?=
 =?utf-8?B?N2dHcy9BK0hXVWREMlI0b2FHTzVpTnh0QS9mUW9LaHZxWHpxOVdKdG82Rnho?=
 =?utf-8?B?c1FuY1RIK0ZHb0RDSnV3bkN6Sjd4WUwzVW91Ymwzd3VaQktPNE5UQVJvYi8y?=
 =?utf-8?B?V3pBRzFZdHFicFJFSStlWVlBSWZyT21Kdko4NVNuOVVuMmZuU3BZSDZUMzJX?=
 =?utf-8?B?TWZSTVc0VW5kRzhDb3lXdk1VSDd1djkzUEUwWitaWkFyRmkrT0FNMnlJbFVL?=
 =?utf-8?B?MHNIVHc2aGlTKzVIc1NEdzZheW53ZTZOQkx2VWw4bmFrNEhrMVZWd2JndGlW?=
 =?utf-8?B?VzZHOU42OThYUnZZT3FhK2gybWFvYVVHTWJkRHJsZEt5MVNZaTJRcjJnbHlI?=
 =?utf-8?B?eE50UnIvTURPTzFQeENqQ1NDRzJpSmlJQlVKVERyeDRkWDhOMVNTWE1Nc3VK?=
 =?utf-8?B?cW12VndBTGdWSEJYeGJDYXhBcjhhZXdwTkNVWEQ1d2dvR1JDT1BpdkJDZTRs?=
 =?utf-8?B?Mk1wa1hJY0F1V0tTcitBbC9tdzBtODU4WnhlRnRiVkNNV2JVVGptU1N0OUJF?=
 =?utf-8?B?b0JrQ2l2VFlVTXJvSTM5UTNoTDhmUVRDcmN4QW0veUM0eHpVUk9yY1dRVEtn?=
 =?utf-8?B?ZTJZckdCZC9oTFo0VEZrR3JrTC84aUhuN0R6U2k4VmIzVWdFV2wyQkZCSnYr?=
 =?utf-8?B?UzR6SXYzZTZQUkFIa3JxQUd5NzhqNlZnSi9qcE1DRCsrejJUUXBWcy8xZGZ0?=
 =?utf-8?B?bHRrd2tHUmdKeURuaHl3Yy83cllxSzRRbVg4Z05zdFpiTFd2SjlGeUl6N01m?=
 =?utf-8?B?SWZ0L1k0TnZkRzJ3OGhhQ1JzM3ZkOUMzdTBQSit6ZkxvS2Nob3dSWGZzQ1Bq?=
 =?utf-8?B?V3hQZGcveW1ndWJvRTMyVVJ2WTZrYUIzejdDQ2hvdUVDM1JYLzJYeHNVL1ZQ?=
 =?utf-8?B?K0JVMEVmK2ZNc1dZNnlteCs2ZlJiM0ZzQTZaV2R6VmtRT3h6d1JyNTlscDhn?=
 =?utf-8?B?RXc9PQ==?=
X-MS-Exchange-CrossTenant-Network-Message-Id: 17ec20b4-aa48-4775-e637-08dc5a4e5d74
X-MS-Exchange-CrossTenant-AuthSource: SJ2PR11MB7573.namprd11.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 11 Apr 2024 17:39:40.2753
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: 4fDIzPA+Tt2ddq0YgzdNbfrRu9CfNq4nCiAa72znf0iGTLnX8i1Jg0uuxFzeeRjfuPkAAKIwY0D2kaiRuS1KVQteYz3gZvMatTNoAz9WYfA=
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN9PR11MB5225
X-OriginatorOrg: intel.com

Hi Dave,

On 4/11/2024 7:17 AM, Dave Martin wrote:
> On Mon, Apr 08, 2024 at 08:23:36PM -0700, Reinette Chatre wrote:
>> 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?
> 
> This sounds plausible.
> 
> In a recent snapshot of James' MPAM code, it looks like we could be
> initialising rdt_resource::mbm_cfg_mask when setting up the rdt_resource
> struct for resctrl, though in fact this information is captured
> differently right now.  I'm sure why (though James may have a
> reason). [1]
> 
> I don't see an obvious reason though why we couldn't set mbm_cfg_mask
> and detect bad config values globally in mon_config_write(), the same as
> for the existing AMD BMEC case.
> 
> Nothing in the MPAM architecture stops hardware vendors from randomly
> implementing different capabilities in different components of the
> system, but provided that we only expose the globally supported subset
> of event filtering capabilities to resctrl this approach looks workable.
> This consistent with the James' MPAM code deals with other feature
> mismatches across the system today.
> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git/tree/drivers/platform/mpam/mpam_resctrl.c?h=mpam/snapshot/v6.7-rc2#n730

My response was based on what I understood from the goal of this change
as described by the changelog. The patch does not appear to match with
the goals stated in changelog.

As I understand the patch it aims to detect when there is an invalid
event id. It is not possible for this scenario to occur because this code
is always called with a valid event id.

Reinette