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Peter Anvin" , Andy Lutomirski , Jens Axboe , Christian Brauner , Peter Zijlstra , Shuah Khan , Arnd Bergmann , Jonathan Corbet , Ashok Raj , Jacob Pan , "Gayatri Kammela" , Zeng Guang , "Dan Williams" , Randy E Witt , Ravi V Shankar , Ramesh Thomas , , , , References: <20210913200132.3396598-1-sohil.mehta@intel.com> <20210913200132.3396598-4-sohil.mehta@intel.com> <87lf3nexrz.ffs@tglx> From: Sohil Mehta Message-ID: <42a14757-5b38-19cf-d830-1641b07f89ba@intel.com> Date: Mon, 27 Sep 2021 13:42:33 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Firefox/78.0 Thunderbird/78.14.0 In-Reply-To: <87lf3nexrz.ffs@tglx> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-ClientProxiedBy: BY3PR03CA0020.namprd03.prod.outlook.com (2603:10b6:a03:39a::25) To BYAPR11MB3320.namprd11.prod.outlook.com (2603:10b6:a03:18::25) MIME-Version: 1.0 Received: from [192.168.86.37] (73.222.31.188) by BY3PR03CA0020.namprd03.prod.outlook.com (2603:10b6:a03:39a::25) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4544.13 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?UUVidS9nRTdyVFpmc3hqWHdKMXpZeXN2aEJjdXlCWmRGVFB4bTh2ZlozUTF4?= =?utf-8?B?cXZKNjg1TnBCSHRFYkxIVVJyZXVpMXpaZmI3WjhhTXdLekkwODJ2OHUrRDBX?= =?utf-8?B?SjNMallleHdLQTZENEoyYTZQYnRKbDdZWG43cUMraXlJdk1Vc3ZYb0hDMVFX?= =?utf-8?B?Ky9FSDB0NCtZaU9YZ2dmbWwxUWtMcHFvdFVPQWhJbWxsRkxsS0VKT2Q1S3pq?= =?utf-8?B?YVpVZUo0YVhwcmRkZGNVUU5TTGFSY1k5djlVNkFCV2ZnQjlCQUZMWlRyQ2U0?= =?utf-8?B?bnlCbDBKT1lFVGp5ZzM3Rk1KMjdSV1g5Nms0TVd3Ym9ZRUZlOFN4NEhDMmhS?= =?utf-8?B?MzYyOGJiUEJrczFZSHFXa0IwbklsWEc1RmQ0dXhGMlJvRXZ3UHdLZ1crZ0pj?= =?utf-8?B?dGF3Vi9XZU1iVUVRdzhyeHZHMVNjVTVpcWZtazNoT1FkelFyaXoxZmFadlNv?= =?utf-8?B?dWRzUU9sN0ZXWVVHaWJzSzNPdWkwUGcvOVhUdW9VUUJuUE5Ha2l3aEtsN2F3?= =?utf-8?B?MlVzSERRdldYWEFYZzZBWVFwc2ErQThFLzVWNDNmbWZvZHlMTGpFb2p3Q044?= =?utf-8?B?SEcwaEpSaXZnRFlKNHdoWGxFaUVvbXhEcmcvdXRoZy9tMzhJVWxOZFllY0JW?= =?utf-8?B?cEpjcWIvS0NhOE5zdnd2bE5xY01EcWhOalFmUEtGKzhQYldvUW1WS0psSXd4?= =?utf-8?B?d3c4MHFKQWhKOW1LcFJJdmhLZk0vSXRoc01adHlUZm53U0dTNk9FZWVzTC85?= =?utf-8?B?ZEJobXBBVU9RaVJQbWFHeksrb3ZOS2Z5WXJaVm52UGV6d09SN053U3RvK25J?= =?utf-8?B?YVRLVWRsYXJZb1pqazdyS0ZURzdDNlB4UjliViszLzlQYVNiakgyM3o4S0hu?= =?utf-8?B?aGZFcWViV3FtN1h1aDUrQVNZUFY1WTl4cU5qUHI3dUZLNU1EZUFwcVMzeHM3?= =?utf-8?B?WVpPaU9yUHJDUHd2OVJFYkY0dE5vcG01M3JBdXdHcUZYNmt0cEVMeDg0by92?= =?utf-8?B?OEFubnRDSllqT3JIYXllTFlmdmxFY1ZXemE4RVh1cUR4OVJCKzIyMDJ5eHRU?= =?utf-8?B?Qkl0dG1ucjFnNnFhRGhFMTBRczRTMjRvRFhWUG5tcldVc0dzc0RIYWxWZzdv?= =?utf-8?B?TGg5TWZ4OUx0WGlxYkgwVWxsMUtYSS82OFBYdFZOY2psYXdjUVFheTVySXhM?= =?utf-8?B?TG83MjVOQzFPRnk2U2dML05zUmVEMHRVcURmaGt0dlRVTmszR2libUtwT21R?= =?utf-8?B?L2ppOVN6SFlTMmFremxvRTJ5OEdMSms2TXBkNVBnKzJ3ejVVYkZPT1dtcWxm?= =?utf-8?B?bklhdnBua1h2NVBxdlhncGVaN2FlS3JuUEkwUE9zOEpSM1RVWVlXU1hxTXJr?= =?utf-8?B?dWhCTnNzQ0JZSm1DSWlqMnVSZmpPaTNOTlNRVTFudDVLejJTUjZaejRWZm4r?= =?utf-8?B?M042RzhFUCtKVzdpYWhDcS9ZbUt1K1N2WEFQaWI2QUlQbWsxa0hEMmZ5WEla?= =?utf-8?B?Skx4NFpVaHpZeXpzRkQzK1paVUxhZVJCOE1kVmMrVittZUd0bEd2S3MraGJT?= =?utf-8?B?eUEyd2VzNzZjZG1GVUt2d21FSVM2VHNCRlRodG94Q25ScXF3am9ldTIzWm9S?= =?utf-8?B?aVpLSFROQjZ1VElabmhzTmVPNlRCR01PSFhVVEJiYk1CU1lXTEpwUDFoWW5o?= =?utf-8?B?UGo2SWZaWEFwT1pYRFRrRWxjRFBHaEdIcUZOQUt6aHZ0bjduSkVrWGZQeFBQ?= =?utf-8?Q?oeIGKz/YLXbIuKHMGQv1GV0PxLl6hvvXOuwpt8x?= X-MS-Exchange-CrossTenant-Network-Message-Id: 2b7c9686-96b1-43e5-8da2-08d981f75655 X-MS-Exchange-CrossTenant-AuthSource: BYAPR11MB3320.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 27 Sep 2021 20:42:35.8166 (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: 6oaVzGaLncIi1udGLYff3TcM6LhFjeZGLoT0YfA0XRwyjXew1OhRgR07BtLJyl+GL9Bdgq4m4BIm2WbB93lnWg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: BY5PR11MB3927 X-OriginatorOrg: intel.com Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On 9/23/2021 3:24 PM, Thomas Gleixner wrote: > On Mon, Sep 13 2021 at 13:01, Sohil Mehta wrote: >> SENDUIPI is a special ring-3 instruction that makes a supervisor mode >> memory access to the UPID and UITT memory. Currently, KPTI needs to be >> off for User IPIs to work. Processors that support user interrupts are >> not affected by Meltdown so the auto mode of KPTI will default to off. >> >> Users who want to force enable KPTI will need to wait for a later >> version of this patch series that is compatible with KPTI. We need to >> allocate the UPID and UITT structures from a special memory region that >> has supervisor access but it is mapped into userspace. The plan is to >> implement a mechanism similar to LDT. > Seriously? Are questioning why we should add KPTI support if the hardware is not affected by Meltdown? or Why use an LDT like mechanism to do this? I have listed this as one of the opens in the cover letter as well. I am not sure if users who force enable PTI would really care about User Interrupts. Any input here would be helpful. > >> + if (!cpu_feature_enabled(X86_FEATURE_UINTR)) >> + goto disable_uintr; >> + >> + /* checks the current processor's cpuid bits: */ >> + if (!cpu_has(c, X86_FEATURE_UINTR)) >> + goto disable_uintr; >> + >> + /* >> + * User Interrupts currently doesn't support PTI. For processors that >> + * support User interrupts PTI in auto mode will default to off. Need >> + * this check only for users who have force enabled PTI. >> + */ >> + if (boot_cpu_has(X86_FEATURE_PTI)) { >> + pr_info_once("x86: User Interrupts (UINTR) not enabled. Please disable PTI using 'nopti' kernel parameter\n"); > That message does not make sense. The admin has explicitly added 'pti' > to the kernel command line on a CPU which is not affected. So why would > he now have to add 'nopti' ? Yup. I'll fix this and other issues in this patch. I thought the user should know why UINTR has been disabled. In hindsight, this would have been better covered in the sample Readme or something similar. Thanks, Sohil