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X-MS-Exchange-CrossTenant-Network-Message-Id: 8f268ee3-efbf-4c5b-a404-08dbce55c5e9 X-MS-Exchange-CrossTenant-AuthSource: MW4PR03MB6428.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 16 Oct 2023 14:39:59.2823 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 335836de-42ef-43a2-b145-348c2ee9ca5b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: PDAy7ZlBUCmbaxO/2OgdoDUPjglexJoBqXrK8Gx9VJjFtWlUC01ipNA3Kvsggqvjz2AQ3/2shNL89Fkvd0Zkdw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS7PR03MB5413 On Mon, Oct 16, 2023 at 04:04:34PM +0200, Jan Beulich wrote: > On 16.10.2023 16:01, Roger Pau Monné wrote: > > On Mon, Oct 16, 2023 at 03:58:22PM +0200, Jan Beulich wrote: > >> On 16.10.2023 15:00, Roger Pau Monné wrote: > >>> On Mon, Oct 16, 2023 at 02:35:44PM +0200, Jan Beulich wrote: > >>>> On 06.10.2023 15:00, Roger Pau Monne wrote: > >>>>> --- a/xen/common/domain.c > >>>>> +++ b/xen/common/domain.c > >>>>> @@ -1998,6 +1998,10 @@ long common_vcpu_op(int cmd, struct vcpu *v, XEN_GUEST_HANDLE_PARAM(void) arg) > >>>>> { > >>>>> struct vcpu_register_runstate_memory_area area; > >>>>> > >>>>> + rc = -ENOSYS; > >>>>> + if ( 0 /* TODO: Dom's XENFEAT_runstate_phys_area setting */ ) > >>>>> + break; > >>>>> + > >>>>> rc = -EFAULT; > >>>>> if ( copy_from_guest(&area.addr.p, arg, 1) ) > >>>>> break; > >>>> > >>>> ENOSYS is not correct here. EPERM, EACCES, or EOPNOTSUPP would all be more > >>>> correct. > >>> > >>> I don't think so, common_vcpu_op() default case does return -ENOSYS, > >>> and the point of this path is to mimic the behavior of an hypervisor > >>> that doesn't have the hypercalls implemented, hence -ENOSYS is the > >>> correct behavior. > >> > >> Besides that other ENOSYS being wrong too, I question such "mimic-ing". > >> Imo error codes should be the best representation of the real reason, > >> not be arbitrarily "made up". > > > > The point is for the guest to not take any action that it won't take > > on an hypervisor that doesn't have the hypercalls implemented, and the > > only way to be sure about that is to return the same exact error code. > > I don't follow this kind of reasoning. Why would a guest, whose code to > use the new sub-functions has to be newly written, key its decision to > the specific error code it gets, when at the same time you expose > feature bits that it can use to decide whether to invoke the hypercall > in the first place. Because we don't control all possible guest implementations out there. AIUI the point of introducing a way to disable the newly added hypercalls is to make the interface between a Xen previous to the introduction of the hypercalls vs a Xen that has the hypercalls disabled equal, and that requires returning the same error code IMO, or else interfaces are not equal. Thanks, Roger.