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Tue, 24 Mar 2026 17:19:02 +0000 Message-ID: <8cba266d-4d3d-4058-a4b4-b937395e50e3@intel.com> Date: Tue, 24 Mar 2026 10:19:00 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/2] x86/fred: enable FRED by default Content-Language: en-US To: "H. Peter Anvin" , Xin Li CC: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , , "Peter Zijlstra (Intel)" , Kees Cook , "Ahmed S. Darwish" , References: <20260323201510.1537333-1-hpa@zytor.com> <84489fd4-aa23-4ba1-b5a1-c1baafb6718d@intel.com> <927AE575-3C10-427E-9C4B-0238CBF8301E@zytor.com> <763cbc92-fda0-454e-a2dd-919671db15c3@zytor.com> <1fb5ae44-d443-414f-9d63-3efce4b73bc9@intel.com> From: Sohil Mehta In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SJ0PR03CA0280.namprd03.prod.outlook.com (2603:10b6:a03:39e::15) To DS0PR11MB7997.namprd11.prod.outlook.com (2603:10b6:8:125::14) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS0PR11MB7997:EE_|BN9PR11MB5322:EE_ X-MS-Office365-Filtering-Correlation-Id: 029c1778-2849-4f78-3adc-08de89c971a9 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|7416014|376014|366016|56012099003|18002099003|22082099003; X-Microsoft-Antispam-Message-Info: NePlREg3MR4iRGH3K/0Yp656f9e7V3F03REXryDqBfskv/hLNNOyuNLs5PCpu5uTDgjp+zdqxE3TJhVaz2t/iACcTLG/WQMNOdOKwQp6KEqlLGts9rXw/meHR2YIfLq/hYwxel8dLsPeGvnCU+03DUWgKvfZP/SHvc5/hzqT94QfZTtIfbrfv/l/bLjg0uImSATNTu/aAEWzXFCjSi/+382JcRoytXtfgu87NPLMfzWVtftl+2uXAOHanG6Y5sO0RwZeatXSC7OSEFaxuiFGbVX9qUHkPpmU8EXK0wal8dI9XHSdhRdVOvYRYkaFXnpUrWXqrOFIINe+0phfWJyXivJIqZHcd7lIBT1hPQDuSunGoivys6wF5lDnhJ0PGYn+b+FoTCMgtGVq80iSZUOMsdps3ZLYCZHujLZKEju0+gKp5cIldYOnRNQyVCy0Jb45Htnco3W5XrK0JJumnuj0LNqBECRzNnuqwebhuVLp/T/8LhZ3zjUNwm2NhNmC3h2OVWruswxGVpRMR28o5YpFrYKKKjldLcwA65fOS2bQ1zkyrqWktWb0UZaCm6i4sz5TjJupi22zFnNJIHCHAJdV4WwcA9ybojjooFs3BvS9owWwDn/26lMk94JDrDx5euU+TPF4chLdHZsoz1cGeVJcnABrr7GJQSFK6kNP34AUWxTX9HpnVNLvhSJHUfiYsEW4n/atJurfWHwRw15DwOQL4MnmPyjZXcoM7UIJQxhhOWo= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:DS0PR11MB7997.namprd11.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(1800799024)(7416014)(376014)(366016)(56012099003)(18002099003)(22082099003);DIR:OUT;SFP:1101; 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Peter Anvin wrote: Giving it one last try if I can change your mind :) > On March 23, 2026 10:08:42 PM PDT, Sohil Mehta wrote: >> On 3/23/2026 8:52 PM, H. Peter Anvin wrote: >>>>> Nit: Would it be better to compare with "off" rather than not on? >>>> >>>> +1 :) >>>> >>> >>> It would change the meaning of something like "fred=0" though. >>> >> >> I don't believe we have ever supported fred=0 or fred=1, did we? >> >> Also, I am not sure about letting userspace be creative with command >> line parameters :) For example, fred=yes and fred=enable will both pass >> the same check and cause FRED to be disabled. > > Unfortunately right now we *are* being creative: anytime but the exact string "on" disables FRED. You are right, we are accepting invalid inputs today. There is a slight difference though. The default right now is FRED disabled. So any invalid input would not change the kernel default. Only fred=on enables the feature. With FRED proposed to be default on, I think we should match the above and only let fred=off disable it. All other inputs should be ignored. > This is a general problem. I agree. In general, we shouldn't even need special command line parameters to *disable* features. clearcpuid=fred would have been equivalent to fred=off if it didn't taint the kernel. I don't know the exact history about why the taint is needed. > In the kernel; overall I feel promoting foo= syntax for booleans, which was not the original style, was a mistake, but here we are. > > Anyway, I don't have a strong preference and I think we can leave that policy decision to the maintainers. > Yes, that's completely fine with me. I won't push for it any further.