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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 19 Apr 2023 08:20:50.2063 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: ea619a0e-4007-48af-86f8-08db40aefc34 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[63.35.35.123];Helo=[64aa7808-outbound-1.mta.getcheckrecipient.com] X-MS-Exchange-CrossTenant-AuthSource: AM7EUR03FT045.eop-EUR03.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AS8PR08MB9148 Hi Jan, > On 19 Apr 2023, at 09:52, Jan Beulich wrote: >=20 > On 19.04.2023 09:31, Bertrand Marquis wrote: >> Hi Jan, >>=20 >>> On 19 Apr 2023, at 08:28, Jan Beulich wrote: >>>=20 >>> On 18.04.2023 16:25, Julien Grall wrote: >>>> On 18/04/2023 14:13, Bertrand Marquis wrote: >>>>> On this serie I would like to open a discussion on how to handle the = vector size >>>>> and the corresponding command line / configuration / device tree para= meters. >>>>>=20 >>>>> In general the user must either give a vector size it wants or has a = solution to >>>>> just request the maximum supported size. >>>>>=20 >>>>> In the current implementation if a size bigger than the supported one= is provided: >>>>> - we silently disable SVE for dom0 >>>>> - we silently disable SVE for dom0less >>>>> - we do not create a guest when done through tools >>>>>=20 >>>>> This is not completely coherent and i think we should aim for a coher= ent behaviour >>>>> unless we have arguments for this status. >>>>=20 >>>> +1. >>>>=20 >>>>> Is there any good reason to silently disable for Dom0 and dom0less on= ly ? >>>>>=20 >>>>> I see some possible solutions here: >>>>>=20 >>>>> - modify parameter behaviour to use the supported size if parameter i= s bigger than >>>>> it. This would at least keep SVE enabled if a VM depends on it and co= uld simplify >>>>> some of the handling by using 2048 to use the maximum supported size. >>>>=20 >>>> My concern with this approach and the third one is the user may take=20 >>>> some time to realize the problem in the xl.cfg. So... >>>>=20 >>>>>=20 >>>>> - coherently stop if the parameter value is not supported (including = if sve is >>>>> not supported) >>>>=20 >>>> ... this is my preferred approach because it would be clear that the=20 >>>> value passed to Xen is bogus. >>>=20 >>> I did say earlier on that this comes with its own downside of preventin= g >>> boot to complete for no real reason. It's all Arm code, so you're fine >>> to ignore me, but in similar situations elsewhere (sorry, don't recall = a >>> concrete example off the top of my head) we've aimed to allow the syste= m >>> to boot, for the admin to then take corrective action if/as needed. >>=20 >> But a guest depending on the feature will just crash later when booting. >> This is making the assumption that guests are all able to properly adapt >> to different hardware possibilities.=20 >> This might be the case when you have a full Linux but if you consider an >> embedded use case, if something is activated due to command line paramet= ers >> or configuration ones, it should not be expected that those are ignored = I think. >>=20 >> There are definitely 2 different needs here, maybe we need to have somet= hing >> like a "strict" switch to allow both use cases ? >=20 > Possibly. Yet along what I've said before - would you then also mean that= to > fail boot upon encountering entirely unknown command line options? I think this should depend: - completely unknow: we can ignore - not supported (sve while sve is not supported by the platform or Xen): we= should not ignore I agree that one could use custom command line arguments for lots of reason= s (in linux you can do that and get them back from /proc for example) but sil= ently ignoring a parameter that is known to Xen i do not think we should do. I think in most cases, one could think its system is correctly running but = could get problems later (or in some cases even not have any) so having a clear error= at the beginning is a lot more clear. Bertrand