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Date: Fri, 31 Oct 2025 14:15:22 +0100 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: Jan Beulich Cc: "xen-devel@lists.xenproject.org" , Andrew Cooper , Oleksii Kurochko Subject: Re: [PATCH v2 for-4.21 0/2] x86/AMD: deal with RDSEED issues Message-ID: References: <272093dc-c97c-434a-9977-ad1c26e7e229@suse.com> <68e28e41-e835-4985-80a3-6a99b3d7dc3e@suse.com> <8c7881d9-5959-41b5-865d-d61199ac7a44@suse.com> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <8c7881d9-5959-41b5-865d-d61199ac7a44@suse.com> X-ClientProxiedBy: PR1P264CA0096.FRAP264.PROD.OUTLOOK.COM (2603:10a6:102:345::11) To DM6PR03MB5227.namprd03.prod.outlook.com (2603:10b6:5:247::22) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM6PR03MB5227:EE_|CH5PR03MB7934:EE_ X-MS-Office365-Filtering-Correlation-Id: 591ef11c-8a5c-4940-8099-08de187f8ea4 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|366016|1800799024; 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If an override was in place on > >>>> the source host, an override will also need to be put in place on the destination > >>>> one. > >>> > >>> But they may be malfunctioning before already, if started on a > >>> vulnerable hosts without this fix and having seen RDSEED? > >> > >> Yes. But there could also be ones coming from good hosts. Imo ... > >> > >>> IMO after this fix is applied you should do pool leveling, at which > >>> point RDSEED shouldn't be advertised anymore. Having the feature in > >>> the max policy allows to evacuate running guests while updating the > >>> pool. Otherwise those existing guests would be stuck to run on > >>> non-updated hosts. > >> > >> ... we need to err on the side of caution. > > > > While I understand your concerns, this would cause failures in the > > upgrade and migration model used by both XCP-ng and XenServer at > > least, as it could prevent eviction of running VMs to updated hosts. > > > > At a minimum we would need an option to allow the feature to be set on > > the max policy. > > That's where the 3rd patch comes into play. "cpuid=rdseed" is the respective > override. Just that it doesn't work correctly without that further patch. Won't using "cpuid=rdseed" in the Xen command line result in RDSEED getting exposed in the default policy also, which we want to avoid? Or am I getting confused on where "cpuid=rdseed" should be used? > > Overall I think safety of migration (in this specific > > regard) should be enforced by the toolstack (or orchestration layer), > > rather than the hypervisor itself. The hypervisor can reject > > incompatible policies, but should leave the rest of the decisions to > > higher layers as it doesn't have enough knowledge. > > But without rendering guests vulnerable behind the admin's back. I think that's part of the logic that should be implemented by the orchestration layer, simply because it has all the data to make an informed decision. IMO it won't be behind the admin's back, or else it's a bug in the higher layer toolstack. Not putting rdseed in the max policy completely blocks the upgrade path, even when a toolstack is possibly making the right informed decisions. I guess I need to see that 3rd patch. Thanks, Roger.