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Mon, 16 Mar 2026 20:27:21 +0000 Message-ID: Date: Mon, 16 Mar 2026 13:27:18 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/2] x86/cpu: Disable CR pinning during CPU bringup To: Dave Hansen , "Nikunj A. Dadhania" , Tom Lendacky , Borislav Petkov CC: , , , , , , , , , , , References: <20260226092349.803491-1-nikunj@amd.com> <20260226092349.803491-2-nikunj@amd.com> <20260309134640.GOaa7PQJli_C9QATGB@fat_crate.local> <20260309161516.GAaa7yFMulhdzNQ-pt@fat_crate.local> <70644e1d-dd0e-4f0f-81c0-fd095e46e50b@intel.com> <7ca205d6-b01b-4ed3-959d-db31a6496d79@amd.com> <505a6bbd-3ecf-4de9-8fb9-0b21c3435a96@intel.com> <9fa61b80-0e16-4a87-a0e7-3c3dfcda8f7e@amd.com> <55a98b6d-e831-47a6-aa5a-8fe357334f67@intel.com> Content-Language: en-US From: "Chang S. 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Dadhania wrote: >> 1) Back-porting complexity: The current issue affects kernels (6.9+) >> where SEV-SNP guests fail to boot with FRED enabled. A simpler fix would >> be easier to backport and verify across stable branches. > > The simplest fix is to disable FRED on those kernels, fwiw. In addition to this, On SEV systems, early exceptions appear to be expected in practice while CR4.FSGSBASE=0. So, at the moment, it also looks safe and simple to disable the feature until when those entry paths are adjusted to tolerate that case. Currently, those entry paths are patched to use FSGSBASE instructions regardless of the CR4 setting. That inflexibility appears to make it broken in the first place. I’d take a look and come back with something reviewable.