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Peter Anvin" , linux-kernel@vger.kernel.org, Pavin Joseph , Eric Hagberg , Simon Horman , Eric Biederman , Dave Young , Sarah Brofeldt , Russ Anderson , Dimitri Sivanich , Hou Wenlong , Andrew Morton , Baoquan He , Yuntao Wang , Bjorn Helgaas , Joerg Roedel , Michael Roth References: <20240520183633.1457687-1-steve.wahl@hpe.com> <20240613152826.GKZmsQGnO3OthLH3Vu@fat_crate.local> <20240616202533.GDZm9KPZtpDKw5aXWX@fat_crate.local> <20240621131742.GEZnV9dn_0XVH0IZ58@fat_crate.local> From: "Kalra, Ashish" In-Reply-To: <20240621131742.GEZnV9dn_0XVH0IZ58@fat_crate.local> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SA9P221CA0007.NAMP221.PROD.OUTLOOK.COM (2603:10b6:806:25::12) To SN6PR12MB2767.namprd12.prod.outlook.com (2603:10b6:805:75::23) 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: SN6PR12MB2767:EE_|PH8PR12MB6771:EE_ X-MS-Office365-Filtering-Correlation-Id: 01956b06-3744-4b37-610b-08dc922a2b3f X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230037|376011|7416011|366013|1800799021; 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I.e. This is a stroke of >> luck, > Ya think? > > It is more likely that I win the lottery than finding such a beast. ;-\ > >> and for all I know could depend on configuration such as memory >> size in addition to motherboard and BIOS version. However, it does >> not seem to change from boot to boot; as system that has the problem >> seems to be consistent about it. >> >> Second, boot linux including the "nogbpages" command line option. >> >> Third, kexec -l --append= >> --initrd=. >> >> Fourth, kexec -e. >> >> Systems that have this problem successfully kexec without the >> "nogbpages" parameter, but fail and do a full reboot with the >> "nogbpages" parameter. >> >> I wish I could be more exact, > Yes, this doesn't really explain what the culprit is. > > So, your 0th message says: > > "But the community chose instead to avoid referencing this memory on > non-AMD systems where the problem was reported. > > commit bee6cf1a80b5 ("x86/sev: Do not try to parse for the CC blob > on non-AMD hardware")" > > But that patch fixes !AMD systems. > > Now you're basically saying that there are some AMD machines out there where > the EFI config table doesn't get mapped because it is somewhere else, outside > of the range of a 2M page or 1G page. > > Or even if it is, "nogbpages" supplied on the cmdline would cause the > "overlapping 2M and 1G mapping to not happen, leaving the EFI config table > unmapped. >From the instructions to reproduce this issue, it looks it is only reproducible on some AMD systems with the "nogbpages" parameter supplied on the kexec-ed kernel's command line, so supplying "nogbpages" is essential to reproduce this, but then "nogbpages" as mentioned makes sense on Atom processors mainly and those are already safe due to the following commit/patch: commit bee6cf1a80b5 ("x86/sev: Do not try to parse for the CC blob on non-AMD hardware") The question is why would you want to use "nogbpages" on AMD systems and then find one of this system which does not have EFI config table mapped as it is outside the range of a 2M or 1G page. Thanks, Ashish > > Am I on the right track here? >