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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=nINN8uLBn/KX27mhSapKsCS5RQcml78jX28DdteYTB8=; b=gizxa8e/Kr8uvOdhDYiJ4qolNUttvLAhc4bawx6CEcaBGfWXlqlwsA7hgGBPAKxroire2N/d63oi2IntB2uHpXZ/rwKdcNXyDZZLcvKEvEJpUt2UYlEkwxVvOemVBTnQ0SpKadAGIaHL0If289KKVFk8S7tkPPezGSuxWALFZkY= Date: Mon, 18 Oct 2021 14:52:28 +0200 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: Jan Beulich CC: "xen-devel@lists.xenproject.org" , "Andrew Cooper" , Wei Liu Subject: Re: [PATCH v2] x86emul: de-duplicate scatters to the same linear address Message-ID: References: Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-ClientProxiedBy: LO4P123CA0288.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:195::23) To DS7PR03MB5608.namprd03.prod.outlook.com (2603:10b6:5:2c9::18) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: dfc07811-8f3a-454c-6894-08d9923627dd X-MS-TrafficTypeDiagnostic: DM6PR03MB4058: X-MS-Exchange-Transport-Forked: True X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:10000; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?UUJ4a2c1UVZKSFV1SmE5eXBENWI4cGlTSnlySGhOSncrVytMVEg3RGtvbVFB?= =?utf-8?B?b01QTmJTV1AxanVtZVBsenB3N2hOMDlEQ2tZY0FUenJTUXBRWWtGeUd1cyt6?= =?utf-8?B?Rmh4NEIwM090ZnhlWlN6MjVwb0JyU3gzTzlVa3Bpa2RMeEtSMDVOWVNFOVNQ?= =?utf-8?B?SlJhcnh2MlptOVlnRWNMYnk2SjhxUlJPbC85a0J5aGlVTk1XQ2ovOEdsWklQ?= =?utf-8?B?U09HUll1YXdSUytQekpFdjFWS3lOditEanlpbndteEhNdHc4WitXVjVEQmw4?= =?utf-8?B?VTU0K1pXV2R6bjhraGVWTzVwdnBYSzFtQ2R6bEF0NU5EN0ttTFJ4QyttVTBO?= =?utf-8?B?aFZLL25YYWI0dklqZVNleDV4d2FxK3JvUjNZbk9ITXdhcVREWEx4WmVQdGd3?= =?utf-8?B?T0pUTU9PZEwzaEhxUVFnQjFmRW9YSWpMOWp2WFBZTUIyaGpISkIxL05uc2xU?= =?utf-8?B?cGZWOHlRSFRJcU1sbzd4NnlWK2x6TjJCd2pmVEFVKzdzMlVLb0NrcFdlS0Jr?= =?utf-8?B?N0Q3Nm9YaHZyaE95WjhxMmRCTzVoNitnVVRmblJVN3RzRlBvZUtKenhkUXdY?= =?utf-8?B?aGl0eTFDTXdteW5iOUVYdDhBQ3hpZktiN1loTjhqaDl3akJwZkhDRXNBRGNX?= =?utf-8?B?NTNGNStUamNOc29GaVdtZFl5WVlUUzFiSFI3a3F1T2U1TElhYjQ4QW1vbzY5?= =?utf-8?B?aXhDZFhTeWM4UXJOK3hIRjdaRi9nckx5RjZPb2NyWHdlWDVYUEZwQU1jWlVK?= =?utf-8?B?Ty9yTWovT0RwcDNqTnZhMytBc1pHS1NqY2JDSklyWk0wZTR6TnFzcGtaNWd3?= =?utf-8?B?NUhEd2xDRm52ZDVNOU5PelcwdVR0UGFvVXN6c2kybGpOVlhsdGhHSEVOYWZs?= =?utf-8?B?cWJ6MmZMTllnd3BKUlpYT2Z5alVkblk3ZzZheXRtV01SRGJ1ZnNLZStyTytp?= =?utf-8?B?bGRiSzlrWmdIR0lHckVRWk1rVzFJR3J6MlpxS0lPc0h1UUhDWTIvandwZFRx?= =?utf-8?B?RjJBTFQzZnluRVRSc0JjalF3RDIrNVIycnZHTlNWM2hFdkR3WUZEVFRtM0V3?= =?utf-8?B?YkFaVlJZQ2VBUXR5cUpQOVl3Mm9Jd0M5ZWNnSDJ0elJWbHlhUkM3WGx5MGov?= =?utf-8?B?YUh2RVhSMGcyTTFEL0ZkQ0dXUnhNZTNtRHkzYkJVMlV0SnZsL3c4TWpnZ0h0?= =?utf-8?B?YTFwdysxczYxUGNPZkJlVjhFL2puTEhZNm9qMnZvMVZiblV5eEIyY0s0VTB5?= =?utf-8?B?b0tiaG1NUGZ1ZUpXd3luaWd0S2IzYUxHV3dOcXFKUjM1NUFsdVN4NDZOOWJp?= =?utf-8?B?QWpJc201UHZyZDNaamRUVUp6WWlvSzlHT3dZY0dBZDM5Zkh3a05IdFhPb2ZR?= =?utf-8?B?blpyczQ5d25BRjZGUEJWUHdZYXRBVE1qNWZOL3h0TW5tYkZnaGtsWjhhY3BH?= =?utf-8?B?alJ6RVBpTkpKVTNkbnFLR0NpNVYxVTIwRy9GZTRvNWJFVFdnbkZHd3NEMUwv?= =?utf-8?B?azVsQVJjaE9KUjRxMnR5T0FhaC9WamowWW1hTjc5cXk4VXNiOTB5UjRoVktS?= =?utf-8?B?ZDNLY2dPYnVYYXY5ZWk4V0FRcGU0Snl5NWFvcDhURTlZL3ZRVVhxQ1Q5dnp5?= =?utf-8?B?bHBEdmxnREVqYUJOcERVamY5NGYyRm1WM0o4NmhRd3BmTVJ1akhPVXczR21x?= =?utf-8?B?TWE4cVhmODZOYnZKVkwyRThzM0dJblpxZHZpUlI0S0hWbnl1K05SSkYyb2lP?= =?utf-8?Q?JmaGqr90PE5UiHTqxIMzfNJ4uku7saBM6UGGJ0/?= X-MS-Exchange-CrossTenant-Network-Message-Id: dfc07811-8f3a-454c-6894-08d9923627dd X-MS-Exchange-CrossTenant-AuthSource: DS7PR03MB5608.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 Oct 2021 12:52:34.6497 (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: wMsJfOo6Cpf8386vTxQg89rTm/zbU5bX3GounF4JBWXS6/S0YwaG7UTUyU+8jEB9dcBiA3A4YXV+YbqdESEcgw== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR03MB4058 X-OriginatorOrg: citrix.com On Mon, Oct 18, 2021 at 02:17:39PM +0200, Jan Beulich wrote: > On 18.10.2021 13:19, Roger Pau Monné wrote: > > On Thu, May 20, 2021 at 03:34:28PM +0200, Jan Beulich wrote: > >> The SDM specifically allows for earlier writes to fully overlapping > >> ranges to be dropped. If a guest did so, hvmemul_phys_mmio_access() > >> would crash it if varying data was written to the same address. Detect > >> overlaps early, as doing so in hvmemul_{linear,phys}_mmio_access() would > >> be quite a bit more difficult. To maintain proper faulting behavior, > >> instead of dropping earlier write instances of fully overlapping slots > >> altogether, write the data of the final of these slots multiple times. > > > > Is it possible for a later (non duplicated slot) to cause a fault > > ending the instruction without reaching that final slot that contains > > the written data? > > Yes, but that's not a problem: Only faults are required to be ordered, > and when a fault occurs guarantees are made only towards lower indices > (read: all lower index writes would have completed, while nothing can > be said about higher indices). All non-faulting writes can go out in > any order (unless there are [partial] overlaps, but afaict that case > still gets dealt with within spec by the proposed new logic). Oh, OK, so it's fine for a later write to be 'completed' even if one of the previous ones faulted. In that case: Acked-by: Roger Pau Monné Thanks, Roger.