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mx.microsoft.com 1; spf=pass smtp.mailfrom=citrix.com; dmarc=pass action=none header.from=citrix.com; dkim=pass header.d=citrix.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=citrix.onmicrosoft.com; s=selector2-citrix-onmicrosoft-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=4jEKH8PX/ONb1EVKOuyR6l6EL4AdOivu1ZjE6u1YryU=; b=S2OtcvTiSGn6vZWinWZAhBolgHOrafmijbxh7RaLQXFiROYzwo7HBopYYgxsTBtxTV2gOkDcEPlAe72w5vkPDewkO/puQdQ2S/O4JzAsUq+sezVsA7eZTI+3lyJ+Q2VGZTkHuVvJf6UP5EWGKuVo7pvjtXr6MtK5KqkjEtiwEik= Subject: Re: [PATCH 6/7] xen/evtch: use smp barriers for user event ring To: Jan Beulich CC: Boris Ostrovsky , Stefano Stabellini , Juergen Gross , , References: <20210206104932.29064-1-jgross@suse.com> <20210206104932.29064-7-jgross@suse.com> <2d354cad-3413-a416-0bc1-01d03e1f41cd@citrix.com> From: Andrew Cooper Message-ID: Date: Mon, 8 Feb 2021 10:23:02 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.1 In-Reply-To: Content-Type: text/plain; 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X-MS-Exchange-AntiSpam-MessageData: =?utf-8?B?L2lFWDVidHl0Y09YRGhuS3Jhb1N6WkorM0NJT09aRlFjTjlUTk1TUlQ2T0hM?= =?utf-8?B?YmtVS2hnN05IQllnWlBGWVAydEhUbFd0MjBLelVQQ3laeGdvWlBieERweGxa?= =?utf-8?B?OVNaSVBRVGZiVFZwUnBNY1ZxczJ5a2dQdTVlbWdRcEpsWXVUZ0RrYlJlNC96?= =?utf-8?B?QVYvUjR0UlBRbFJNVzB3a0tFRExBcTNKdUJOTGl0cXNTWlJNK3h3VG5BR1E2?= =?utf-8?B?SGlLR2w1dE1MZXBCVkgzeUFSTXNjdlVENWZvN1psR2xIb1NvYTliMElLazdi?= =?utf-8?B?K3k2QU9xOTVjQVVoc3piSTFkRjdrVFpFL2p0SVM3TUxGd2xIeUdQOXJtbWVu?= =?utf-8?B?NkRXYzZiWVNwREVScUs5U3RnVUZEdUg1NElKK2hWdXYwVmlMakYrbXhCQ3hS?= =?utf-8?B?ODdmUkZPOHNpQWJqQ1pGanVHdnVGdG1veTE4MFBIMjRnb0swdlpRNHBySXUy?= =?utf-8?B?eDVscDBxVXoxaVVIakNRM21BU3dIQ0t0VDhNL1BMaU9TTkJ2WlFEb2ZjcFVj?= =?utf-8?B?ZzY3RU9ST0poTzc5eDgydkIycnViczZFVEFJYkFGRlp0SHRyaXJvZnBDNXBs?= =?utf-8?B?bmFsQjVzYkVSRm1MK2lVTWIwQU1YN2NDbVZKaDZIRDlGeWFYMURuaHR2c3Ir?= =?utf-8?B?Z250Qloza0taZTBkcWZxK0ZhVUxQZ1I0WGhRSCsrZWdJbE4rN3REN3R4ODRG?= =?utf-8?B?Rm1ZOW4xd2h1R2ZNMVhucnJrMmJzZ2NidHk1eGYyN2lGWHQ0Rk80bTJsRFE0?= =?utf-8?B?Sjc3QWNxU2hjNFFXMElhd05qZ2dtbTB3MFB0R1BjVjBuRmJyZHgvTzNRWmFM?= =?utf-8?B?UVVTa0F1bkMyR2p6Tm9iYkwyZm91N3ZzYWwyc2xETVlwRngwOXQxeTFBTkpN?= =?utf-8?B?aHA1Q0o0WDlralRpWDVCSzdBMnJNanZxWlBWT000THp0Uk4zM05zc3c1SzBu?= =?utf-8?B?T0lEQTkzeWc4OGdzcG1TTTNFeUsrRVJmaW41OVRjQk9qSnRHb0Vxa2ZiWGN5?= =?utf-8?B?S2prU3dGdlBxVzMreEZnRlJpaExCem5McmNHOVJoZ0ZnYm80eFZBRWdlSWtp?= =?utf-8?B?TC92ZUlOaW1OWDJDaDNkenlwdERPZFZSUWh1TnVaYnQwdnlhdnFxby9Lc2ls?= =?utf-8?B?eGZHelJKT3pWRzIyWjVxeTZ5WEx5L0JXcDBUa2ZUWkVCN2JVbkNkZy91dm5L?= =?utf-8?B?bzAycUdDS1RQQkdXRFQ3QTRXNThZWk9wRmlvTEtoVnpMcEZnd2F2aGptNWNL?= =?utf-8?B?ZEZ6b1RvV1lFeis5RHMxSHJOcUJsM3ZzaE02bUwxSHFNOW9QaGlPZkpDQ245?= =?utf-8?B?QlZCa3gyeDR3Y2UyMnBBVm1kSGJjc3F3NDdMSDdNNDRpRnFxcGNjcXU3b2xQ?= =?utf-8?B?TjZFZzV5YkMvM1dJR1k3K1FXaU1yRlIwNWpURExWTGgzTWw4OVFnWVYrTnFF?= =?utf-8?B?bnhzVzlORkdwc2lWM3VNYTV4ZFJDaUp5THpWcXV4ZzlwSStoellydVlLbklM?= =?utf-8?B?RUZiY3RnWUdWL1d4VFJQNStVUmxXWjE0anhqZ1NFaUs1S3hyazZNeU5iVXEy?= =?utf-8?B?WDNkcTFTaVF0R2FBajFITGNhN0Q5RHFtb05wVzQvUEp1QVhDVFJFOGl6Z0RB?= =?utf-8?B?VVlNa0RHWit0WEV5ZTRreGo5N29Ua285ZmhLTjhsSjBtb2Z2RjMvSzVBMzlP?= =?utf-8?B?dUJFeE94NnRPRGpnaHFSdFhXbjdTUkg5ajAxalFyNzBvR01RZnZQSy9QcFlt?= =?utf-8?Q?4JsCrkTNMntTFIcIj4qggTZZ0jN6SYqZ5UhOH6q?= X-MS-Exchange-CrossTenant-Network-Message-Id: d8d14eb3-f60b-43c7-d20b-08d8cc1b8797 X-MS-Exchange-CrossTenant-AuthSource: BYAPR03MB4728.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 08 Feb 2021 10:23:08.5241 (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: jnVbszVxZc7qz/ORwnAZE91BQ61RIHMIdcBz+frg+U6Zd3YOs6JrfOk5t9rzqB71Wt44ubMzCS67F+W55dMOySFEJZVOqaLXP4nRq5YfBxY= X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ0PR03MB5518 X-OriginatorOrg: citrix.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. ~Andrew