Received-SPF: pass (google.com: domain of linux-kernel+bounces-136199-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.199.223 as permitted sender) client-ip=147.75.199.223;
Message-ID: <6d563361-87c0-474d-812c-b33e79eacf3a@intel.com>
Date: Mon, 8 Apr 2024 20:24:12 -0700
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH v1 20/31] x86/resctrl: Allow an architecture to disable
 pseudo lock
To: James Morse <james.morse@arm.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>
 <20240321165106.31602-21-james.morse@arm.com>
Content-Language: en-US
From: Reinette Chatre <reinette.chatre@intel.com>
In-Reply-To: <20240321165106.31602-21-james.morse@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?U1VzN2Y5b2oxTVE1aFNVd2NTcUZ3UWI3S3h0cDdCVGxTcEdESHBhS3k3aTNY?=
 =?utf-8?B?SVB2QmJ4Wi85aW5NUTc5L1NxQkljUHZjS0EyWWcwS1hhV0VtMHBldEZ3dFg1?=
 =?utf-8?B?VXdxOVdoVndKWHZ4THZuZld5RUJmaGVmVjlhQVk1c0lKcEEzQVdtaEtEaWhL?=
 =?utf-8?B?YWU5T3RGNG53dTMwNWRXNi8zWGltNUpSS0tPb1JjckF1RjRQUEJYNVlvdytX?=
 =?utf-8?B?c2cwc0dnWDlqb1ZTMUhJMStOZTJjbGxOZGpybXB4RGw0aTRNbHdCZVNRZVVR?=
 =?utf-8?B?aFVHd3ltVkt5RE94aVZDL1gvbkRaR0dpODd0TkYvMjFxaXJnQk5jN3I2b3Y5?=
 =?utf-8?B?M1BwK3lEam1JK3l1T2llRzBLeUJtY0ltNldPaWZWRDd6elRqRysyeVVaOU9r?=
 =?utf-8?B?b1U1Qjk5T2lnWnBiS0t2bWJFSGJxcDIxWHFnM01lUERUNGcvRkJpRUk5YStV?=
 =?utf-8?B?OUJqMER3YnkyelNPZ2hteXlSLzhBV1pBQ09vRGFGRDlFSDd0WlhmT2RCR3Jj?=
 =?utf-8?B?cFQ5VUtwOGZBQkJWNG5oMnR3WmU4Y1ZiV2daMTVDQTdHNXJFdDUvSStCamJJ?=
 =?utf-8?B?bklkMmFEZXB5U2dEMTkxSHhlSk56SW9URWduWG5qMk5EbmhlcUNkQU93dkFt?=
 =?utf-8?B?OHlEUHhUeFQ2VUhRMlVGSWMyaUZCWDhMcHBCMDhwMStOR2NCZUhzTXZibXBq?=
 =?utf-8?B?am5KTzVPRjdQQlVLdFFPQm5xQWo5bFRKVnhVaGNPWkN5QUJnUWJIa0VzVk1R?=
 =?utf-8?B?cWFqSTEwSUExaG1YTWtYNGZUZDl0RWdQMDdwSmFrSFV5aWg1SFdiaTFvUW12?=
 =?utf-8?B?NVEweXVIbTd4aFdzUnJ2TE9nWGV2WnNjdXhGQTBjSkNsNUYweHJaWCtVbjM0?=
 =?utf-8?B?MW1vd3hmRjhnSVV2VXVncmo4cGJXMDhWNS9ZTXZwSVNjdTd0UXdTbTF1SmdJ?=
 =?utf-8?B?L2EyZUtqangzQkFCV2pKbGw1MHAwVzE4WkJkQWhSemZ6U2dGR3JOMjVIcHor?=
 =?utf-8?B?TVg4djlxNy9IbEYyam80MnlHL2M5WkFScnFWWnJ2OVYrdTR6THVxZmd2ZjZQ?=
 =?utf-8?B?UVdKbFBXMkpYZitHNC9BcHlBMXMwY2J4YmE2bXRPVTRqWkZsNDVxNWJLbHl0?=
 =?utf-8?B?QzZaT2Q2ZW9OQ0dNNVYvc3orRjM4MTVBOTV6V2JLYVU2eGJ5bWp2U1RacWJj?=
 =?utf-8?B?K2ljOGNsbm9sREx3RTVhRDlFd3RxVFVSRk4ya3J2d2tHUEo5aFB1TW5QOU44?=
 =?utf-8?B?b204SGhWQ1l2b2FVOFllM2c2Y0FoUTY3alQxWEE1eDVBQ3hXLytPbktoWnh4?=
 =?utf-8?B?Lzh6UENSL1ZiMy91Z3k1YkgwWjNaa1hNVmV6TWVoNktMMXVTODdicVppemZM?=
 =?utf-8?B?MnNITzhQb3ZRTUp5Z25qODJHSXh2N1kxSFp3eWdHRXBFd3o2bWtoQzUyVmxx?=
 =?utf-8?B?bXRwT3ZJUm5JRExKeXdrbzJ1S2ZqSmt6dTlSNFRQQ0hWUm42WElIeWJ0bGgw?=
 =?utf-8?B?QlNmUERGaDE2b0ZIaEluZVJCTnRldUVZRndySW5UaDFxanpQUllTTUlkMHU0?=
 =?utf-8?B?VWZFeDJSOWhMUzQvbjlpQTZEcGtBZXRTRWY2T0V6djlVYVVoTDh3UDJBOEpL?=
 =?utf-8?B?NGRMeG9CMDJIV0NsTmU0VTJYdVhIYlBBQlVXblpIUU9GUzJHa1ZTS2ZFUDhv?=
 =?utf-8?B?aVFWbEtYblNsbWFDRnlxMEJGR2NvczhWQmZxbnFoVW5TeFBIMWhrRUg4Mmsx?=
 =?utf-8?B?TUNtK2ZzamJyQnZNQ05kT3J5Y2h4T01LZXBDQUo1UjdmN1N3NVNORC84TnNx?=
 =?utf-8?B?VC9NUDN4NEpqUUIwUGt3MFZVZkxDMWtHYUdBZmpreGJKbUZMdktNaU5qR0lI?=
 =?utf-8?B?eXh1UGFzWFdzQm1hbmRhaXhoNGRrMlM5dHpLbjRNQ09Rc1gvM01JUmtOend1?=
 =?utf-8?B?MWkyWVpKOXoxcFhJT2NlZTFZRGtIVzQ4WFZoa2ZpMG5Ma0tjNnFsaFRPZ2k5?=
 =?utf-8?B?TEN0SUdkMW9aT0FFTVJReUxBblArWXdNNjFNMVREQ1Uzbi85RStlbm04RWpS?=
 =?utf-8?B?WlBEUGdjYldrNzhWK1ZrSnMybW9wRGprcDhDQUFob1hGK1FuTk4vL21oeDR0?=
 =?utf-8?B?OVV5U092YVhORnFrdExXSG1iUDBwTTN5L1lRUUJKQnlqY2xKTGRBNDY0ajYr?=
 =?utf-8?B?V2c9PQ==?=
X-MS-Exchange-CrossTenant-Network-Message-Id: 3ea33e12-4566-4cc9-5123-08dc5844882f
X-MS-Exchange-CrossTenant-AuthSource: SJ2PR11MB7573.namprd11.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 09 Apr 2024 03:24:14.6517
 (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: psa6E8hMzlDA4AARGaIFYexrPdUq3QkxCvsn0ZLaIWdIPyHVTzQ+WmdJoKIh65qse1BRIp5V/0t/f95l8mGaNf21tLHPzfZliYSAiK5Yvug=
X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM4PR11MB6357
X-OriginatorOrg: intel.com

Hi James,

On 3/21/2024 9:50 AM, James Morse wrote:
> Pseudo-lock relies on knowledge of the micro-architecture to disable
> prefetchers etc.
> 
> On arm64 these controls are typically secure only, meaning linux can't
> access them. Arm's cache-lockdown feature works in a very different
> way. Resctrl's pseudo-lock isn't going to be used on arm64 platforms.
> 
> Add a Kconfig symbol that can be selected by the architecture. This
> enables or disables building of the psuedo_lock.c file, and replaces

pseudo_lock.c

> the functions with stubs. An additional IS_ENABLED() check is needed
> in rdtgroup_mode_write() so that attempting to enable pseudo-lock
> reports an "Unknown or unsupported mode" to user-space.
> 

I am missing something here. It is not obvious to me why the IS_ENABLED()
check is needed. Wouldn't rdtgroup_locksetup_enter()
return -EOPNOTSUPP if CONFIG_RESCTRL_FS_PSEUDO_LOCK is not enabled?

Reinette