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X-MS-Exchange-AntiSpam-MessageData: =?utf-8?B?eWRVTmgyblc0czZUc1d2M0czelduZEN5bTMweEhQdTRGRzBuNWdpdkRmc3ll?= =?utf-8?B?cUNEeGtNTVM5RXdrYlFhMkQ1K2JPTDMvOEdRVFkrRndFQWZESXJiVnZWRTJr?= =?utf-8?B?Wk9nY2wzSzhHVTNyKysyN1NyZmFpT3Y5OWEyYTVnVGtIRzRwQnlvRWd2LzFt?= =?utf-8?B?d3FTdkt3azJOQlJsMmczYzdSK0hFUTBJNFFCUitmaGVBczdKb1BDV1dmVEo5?= =?utf-8?B?cWllcTh5Wkd1N3hxQkFzQW9mVVNJTWtjcDMyaUl3ZkJmVnI2TEtNalNGdE9R?= =?utf-8?B?c0NMOGIyV2t2elFqNHZ3QUNjNVk0THNiUlkxK0N3UGViODhUUkRJSUd6VUlv?= =?utf-8?B?QmZXLzJ3ZENNWGpCYm1Zb0VDQ3N4NkZ0NVlMeGRJY04rdkc5dno0VGF2REg4?= =?utf-8?B?dk1pWDJuMVZvVlRkb2F5Rk0vOUY4UysvdGFxSDk1NGtaM1JjY2VVMGpRVEx2?= =?utf-8?B?MlRYLzZvUTRkR1E2TTcwYlVBT1N5MENaWDZNMFJaVEVlc3BoaDB6dUNIUUQ2?= =?utf-8?B?M0hlMnQ2dGV2ZUVPT3NJcXpHMHZMQ3JSZHVrSkdRMEt2Q0pSWkJFekdvUEV3?= =?utf-8?B?WVkrUHdDK0JxMXhvbVR2cmpJSTh2Q2lHR1RkUHNXVklFMUpmMFdFWC9yTXk0?= =?utf-8?B?UngwWXh4M1A1T0dQQkQ0ZXlzc21FajhTMTdQUk9NLzV3ZzdTQWxFRVlIcURW?= =?utf-8?B?dmJ2OVNTQmpIYTJxbEtHOS9NYTVQanFwekpCNy9URXU1ODdxZXc5ZVBpVEFj?= =?utf-8?B?UklSaHYyMDRnRDlBZEUrVytnSUtJZzBlUlNlVHBYZXh6Z3c5ZzhPVExWOHI4?= =?utf-8?B?RzM1T1g0eHBVL2RLcGFKRTFzZFBpTHJBZ0pJWmI1ZHRqNG5ZbUFGeXU3YThW?= =?utf-8?B?TzI1SFFGekp5RVVCVE9jM3l5QW9lSU8yaGNhMUdCWFZRM1FXaUN0Y0lDOUhQ?= =?utf-8?B?eHcvN1NtMExjZEJuMFUxQ1BlVWwzUFNiS3liOW1kUzVHV1I5ZGx2cVc3RVdU?= =?utf-8?B?aGZpeXlzN1M1bm1oVmw1UUI4dkNWdjJqeXJTa0tkU2VPemk4YUw4Sm9tbTBt?= =?utf-8?B?ajdXTkQ2L2ZVZkhWQS9SOVNjQ29lQStMbW52dHc1aXJvcm5CZjZXa2pSd3dD?= =?utf-8?B?TnN5VW8vVXVFWVF6c1hJVGhGTC9SZENuNHdHZEhNdGJISGdSTVdSa3NERS9D?= =?utf-8?B?V0hZbFptWWNzRkFVczV5VUZNUktUdzd0SDd0c0srWVgxMTNKZThYTWRJMyt3?= =?utf-8?B?c1hvNlIydHJoaTZpeGFEcGY1YUdjWktWNU1UM25yMWw0ZlF6SVVNUEtUcEZC?= =?utf-8?B?dDBneWgxWGloUmZYVnNVTWlvL1huZ243MmFwUEFacHVId0t0dUFMRVlCTGVt?= =?utf-8?B?am5yRUswMG81UkhyZDJ5RWwwNnE4MkM3WG1pVGlTVUFEcVlLcTNrZ2hKMnBG?= =?utf-8?B?LzFnNlFnSWZCWWZvek9yN1F5eDFmQS9MU2s5bWRLNFQ5eldJc3VlWUZCYitu?= =?utf-8?B?VjVsOFBqa2lPcTVPNEppVjdNTmMyZkl0bmxFcGpZbTAzTm03SDVXcFk2WkNh?= =?utf-8?B?US91cmoxSjFTVlRNMWxORlprWm41T1M1ZFJjL1hadG56cXRyZnBZaVlxelZy?= =?utf-8?B?R3BQMGplQ3dEZmhrZjJtQW54VVZkaVpyYVNKVWtzbVlwRDNzcWxkR3UvdXI3?= =?utf-8?B?bDhFUEtVWFVHcDQvNElnUmcxWkEza0R3WHRtUTJqRGdQbXgrRjBqVThGeFNm?= =?utf-8?Q?ZV8sQnEYMRxnkYFhsr37tD7Qx6diu5OQXeQwAf1?= X-MS-Exchange-CrossTenant-Network-Message-Id: 80187434-e7e1-4c8e-9ea3-08d8cc1cb88d X-MS-Exchange-CrossTenant-AuthSource: BYAPR03MB4728.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 08 Feb 2021 10:31:40.1534 (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: YuAdKviTi76TRNXnW7hUxfaEtDBnw5QPNOwPNMiTzDAMBSQUkg7Manjp+ehVuHUMmiuEW07m2cjNC+uume8GZHlU83q1FP9UdhJtUiWOkpA= X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ0PR03MB5823 X-OriginatorOrg: citrix.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/02/2021 10:25, Jürgen Groß wrote: > On 08.02.21 11:23, Andrew Cooper wrote: >> On 08/02/2021 09:50, Jan Beulich wrote: >>> On 08.02.2021 10:44, Andrew Cooper wrote: >>>> On 06/02/2021 10:49, Juergen Gross wrote: >>>>> The ring buffer for user events is used in the local system only, so >>>>> smp barriers are fine for ensuring consistency. >>>>> >>>>> Reported-by: Andrew Cooper >>>>> Signed-off-by: Juergen Gross >>>> These need to be virt_* to not break in UP builds (on non-x86). >>> Initially I though so, too, but isn't the sole vCPU of such a >>> VM getting re-scheduled to a different pCPU in the hypervisor >>> an implied barrier anyway? >> >> Yes, but that isn't relevant to why UP builds break. >> >> smp_*() degrade to compiler barriers in UP builds, and while that's >> mostly fine for x86 read/write, its not fine for ARM barriers. >> >> virt_*() exist specifically to be smp_*() which don't degrade to broken >> in UP builds. > > But the barrier is really only necessary to serialize accesses within > the guest against each other. There is no guest outside party involved. > > In case you are right this would mean that UP guests are all broken on > Arm. Oh - right.  This is a ring between the interrupt handler and a task.  Not a ring between the guest and something else. In which case smp_*() are correct.  Sorry for the noise. ~Andrew