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Date: Wed, 15 Oct 2025 10:00:01 +0200 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: Grygorii Strashko , Jan Beulich Cc: "xen-devel@lists.xenproject.org" , Sergiy Kibrik , Andrew Cooper , Paul Durrant , Alejandro Vallejo Subject: Re: [PATCH v5] x86: make Viridian support optional Message-ID: References: <20250930125215.1087214-1-grygorii_strashko@epam.com> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-ClientProxiedBy: BN8PR15CA0033.namprd15.prod.outlook.com (2603:10b6:408:c0::46) To DM6PR03MB5227.namprd03.prod.outlook.com (2603:10b6:5:247::22) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM6PR03MB5227:EE_|SA6PR03MB7613:EE_ X-MS-Office365-Filtering-Correlation-Id: 5dca0906-a6e9-4207-5f37-08de0bc0d922 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|1800799024|366016; X-Microsoft-Antispam-Message-Info: =?utf-8?B?cUN1ZCtLOTNRNHNJNFI1VmdMbGlJV05uSFBqSFFsRFplY3lRSDNRY0NOSFEy?= =?utf-8?B?VzA5R0ZvSmFxeDVOOVVEM3NMV0pPWVk2V3VUV0JCdENrTE8walZBWkg4V1lK?= =?utf-8?B?blVXUStCcGpJMUFqZUNHUWZRSHBsTXAwajNxK1dGYWd0ZnEra2NuYTdDMmxV?= =?utf-8?B?OWYxQjd5L0liYjNIZTZ1UUJoNENlTDNlakVOSVU3UXRZYUU4bm9VRUhOVDZm?= =?utf-8?B?b2ZSeW50Q0xXV2ltRFc4QlNhMzdGTU1reUJlbWZTM0haSmVLT1RobEdxNndk?= =?utf-8?B?QUpTeXErUFJTaTVCeUNUMHVmZ04ra1NpVG1ld3ZJd0pYdEpQTyt3MVgwTCtr?= =?utf-8?B?SEloQlBzUEhCM1ZaSk0yYnJ2QURRYUQwT2RDTm4yYW91ZTFpa0UrcktnVHZJ?= =?utf-8?B?elErUDlua3NUTFpzaTdJcnpqTUpJcks2OVdreDVsQlpwNzE5a1FEVnFtZXlO?= =?utf-8?B?ZlJOUWZFSVNHamUySXVQZ0p4YmZXTDZJTzYrTnRNK3dCL0RZL3pvb01iVlpZ?= =?utf-8?B?VWc3UEV3TStJUUtCRldWTkdacE5rbFYvcktxZlFiS0dUTkVzZ0NzSXlybmN3?= =?utf-8?B?RW51S0crT3hSR2xZRG5hd0xFRXBWbDZ2N2NlTWJaYlhTQkVJR2kxbm01MXp2?= =?utf-8?B?N1NwOWVCTlJrdEJidjJ1THAvbGhHYjZQRWVwanVZY1dHbHY4UDJmcmpETUVq?= =?utf-8?B?T21vN1JrOFZJempWSHRxYWpVYnY4WmE0MFlFbnJzWmlXeFhqZDV2dXhYcUdx?= =?utf-8?B?WndWQjNMbWlsVnRMRmxqRFdrem8wT3ZBNU41dEZhVGp1KzJQY21sV1FYMjhE?= =?utf-8?B?QTlUM09yS3IydmtodjNkMTlheXZJckt5VXVvZmI3VFhHTWhGaVRHUDRDMDU1?= =?utf-8?B?empVYUdBZFhvdVA5ckJoSFhZUnZaTHNhWDd0aDZHTWFpS1duYlQvdGNvb3k4?= =?utf-8?B?UVNCRzJnRXB6VTVtbS9WZ21PbDVEbUY4Sk4wOEwzTyttZXh2d3cwcmg3dlZV?= =?utf-8?B?RHFlMnRIUDBjeUVObXhIcXJKaTVBZVJTNnhiblBkV0Q3RUlqb1ZoZW1wRmNp?= =?utf-8?B?cGhQTHdjZDZVaU5reFFURDd3ZnBCYVJsTVpyWVRXT0o2Uk94Q09PbWJLdHo0?= =?utf-8?B?SUQ3Y21aMU9ET3pZLzBHWkVxYkxDamhlRncwaUs0cnhzekk2WDJxVnNNN1VF?= =?utf-8?B?dXYvSGFCWWtaRXFEK3R4YkZuTGxqWFFVc2ZJUlkySlVrZUFTd3o0dXZ5eGlG?= =?utf-8?B?N3hYbWxYR3NCSnNlU2xuNmMyam1EMkN4TElqRStPMzZQMjhUSFNIZi9BbDdN?= =?utf-8?B?WXRYVFRsZUtlMkwrcFFrMHVxbmx6UVhUcXZES1ZnQk4rdE9qOEZ0Y1hBUmdi?= =?utf-8?B?YTJjS3JLbGMzSXVzQUdzd3BuMHVFcDEvMWs0NFNBMTYvOTFGQzJOK3lsM2py?= =?utf-8?B?MVlVZG9EQXJRZGFkaGcycFBObEhSNitFSDZRUUduTjJIcDZSUnBKRmMyWEdu?= =?utf-8?B?aDh6bDMwb3NuSFNibEo4cVN6Z0psZU9hUnZicjhvNitKRDVCTGlEOUFSdEZ3?= =?utf-8?B?Qm1jZVN1M3ZkTVlCZUN4QmFNTnE5UlEyeXh2ajg2blZ4N3hmaForc1FzWFhm?= =?utf-8?B?ZElmSGoyQlJ6Si8yMHFjMkdmczhxbms3NEZOTURGcGN4R2FJYTZ3UUQya1RD?= =?utf-8?B?NkpKSDd2ZnJBaDRCOGlyZGh6OEUvbmZ3MXNkY2RTN3YvUTZ3QUdPUUY1WjFh?= =?utf-8?B?U2h5RjIxdmRFRng5TkxZeXo5aWxVSmtsb2dSbWZxcklSNytsU3RXUklRVCtN?= =?utf-8?B?bFI1TVR1M0pWWHBXK0lxKytLYVpvdmZhNEhkOXc2ek5JRVg3TERDbWxzYkV6?= =?utf-8?B?Z1Bwa2hHbDNjbE5lckJzWjdqUzIyVDYwb2xGbXdEYnZxRVY1aGhzYjJDeDZY?= =?utf-8?B?RjJGb3VkbXV5VnFHdkV1dTNraysxdjRGTDVQc3lwREdUMWlQMFQrZWVSdXhO?= =?utf-8?B?bEZZb0NpaHlRPT0=?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:DM6PR03MB5227.namprd03.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(376014)(1800799024)(366016);DIR:OUT;SFP:1101; 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> > > > > - rc = viridian_domain_init(d); > > > > > - if ( rc ) > > > > > - goto fail2; > > > > > + if ( is_viridian_domain(d) ) > > > > > + { > > > > > + rc = viridian_domain_init(d); > > > > > + if ( rc ) > > > > > + goto fail2; > > > > > + } > > > > > > > > Are you sure this works as expected? > > > > > > > > The viridian_feature_mask() check is implemented using an HVM param, > > > > and hence can only be possibly set after the domain object is created. > > > > AFAICT is_viridian_domain(d) will unconditionally return false when > > > > called from domain_create() context, because the HVM params cannot > > > > possibly be set ahead of the domain being created. > > > > > > You are right. Thanks for the this catch. > > > > > > Taking above into account above, it seems Jan's proposal to convert below > > > viridian APIs into wrappers for VIRIDIAN=n case is right way to move forward: > > > > > > int viridian_vcpu_init(struct vcpu *v); > > > int viridian_domain_init(struct domain *d); > > > void viridian_vcpu_deinit(struct vcpu *v); > > > void viridian_domain_deinit(struct domain *d); > > > > > > Right? > > > > Possibly. If you don't want to introduce a XEN_DOMCTL_createdomain > > flag you need to exclusively use the Kconfig option to decide whether > > the Viridian related structs must be allocated. IOW: you could also > > solve it by using IS_ENABLED(CONFIG_VIRIDIAN) instead of > > is_viridian_domain() for most of the calls here. > > > > The wrapper option might be better IMO, rather than adding > > IS_ENABLED(CONFIG_VIRIDIAN) around. > > I'll do wrappers - less if(s) in common HVM code. > > > > > > [1] https://patchwork.kernel.org/comment/26595213/ > > > > > > > > > > > If you want to do anything like this you will possibly need to > > > > introduce a new flag to XEN_DOMCTL_createdomain to signal whether the > > > > domain has Viridian extensions are enabled or not, so that it's know > > > > in the context where domain_create() gets called. > > > > > > In my opinion, it might be good not to go so far within this submission. > > > - It's not intended to change existing behavior of neither Xen nor toolstack > > > for VIRIDIAN=y (default) > > > - just optout Viridian support when not needed. > > > > OK, that's fine. > > > > On further request though: if Viridian is build-time disabled in > > Kconfig, setting or fetching HVM_PARAM_VIRIDIAN should return -ENODEV > > or similar error. I don't think this is done as part of this patch. Another bit I've noticed, you will need to adjust write_hvm_params() so it can tolerate xc_hvm_param_get() returning an error when HVM_PARAM_VIRIDIAN is not implemented by the hypervisor. Implementing the Viridian features using an HVM parameter was a bad approach probably. > Sure. Just have to ask for clarification what to return: > -EOPNOTSUPP (my choise) vs -EINVAL. Let me add Jan also to the To: field so we get consensus in one round. I won't use EINVAL, because that's returned for deprecated parameters also, and when the passed Viridian feature mask is invalid. EOPNOTSUPP is also returned for non-implemented hypercalls, so I'm not sure whether it could cause confusion here, as the hypercall is implemented, it's just the param that's not supported if build-disabled. Maybe ENODEV or ENXIO? Thanks, Roger.