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Date: Wed, 7 Jan 2026 18:22:05 +0100 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: Teddy Astie Cc: xen-devel@lists.xenproject.org, Jan Beulich , Andrew Cooper Subject: Re: [PATCH v1 0/2] x86/pci: MMCFG improvements and always use it if available Message-ID: References: Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: X-ClientProxiedBy: PA7P264CA0372.FRAP264.PROD.OUTLOOK.COM (2603:10a6:102:37c::29) To CH7PR03MB7860.namprd03.prod.outlook.com (2603:10b6:610:24e::14) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH7PR03MB7860:EE_|DS7PR03MB5493:EE_ X-MS-Office365-Filtering-Correlation-Id: 69ec1295-aa52-4369-8103-08de4e114a01 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|366016|1800799024; X-Microsoft-Antispam-Message-Info: =?utf-8?B?T3hVcGxJdERkeXpQVWpVTGlGaGRRaFJNQmFyTXNpUXBHcm5TdFllSFBBVWhX?= =?utf-8?B?Tk1WZVJMS1p6U3RPbjliQ0tpR2hnRFFjaHplOEZLWkl1ZWNmdTh1eit4WmY2?= =?utf-8?B?Yy9vak9EMXJlRGpybDFENHh3R0JVRFhqWEtnb09Tb3p2T3A0c3JGbjhIRUJJ?= =?utf-8?B?NENubHZWYnQ1R1A0MElBekQwdVFieDc3Y2tvbnd5UWxXM2gzdmZHNmRMN3NR?= =?utf-8?B?RUJCOGdYSjRXcld4U1FONDYzUW50N0dOeG56blpPOExvaVJ6K2Yza0RxK3lL?= =?utf-8?B?RkpkZDM5OTlUdzgzVi9tZHMvNjdrK1EwbVpTUXpTalZGVUVSN0hWWURidUhi?= =?utf-8?B?SGRFczBzK1BVUGJCR0J0bzZGSjBuaHdwSStMenN5OUdmcks2S1N4T2g3ZEtt?= =?utf-8?B?NHc4VTVMRTMxRGZlUnJkczRuZjgrQWpyTVJGVEY3YXVWdUdjWGVySVZTYVFU?= =?utf-8?B?cTM4bnZOSE1WMm1jU2lEVm82TWdWV1BNQy9RNDJuN1J0K1RKYTZ2aTVKbzF6?= =?utf-8?B?dGlHQWVqM25Rbk0rTEZQcmplWktKWTByZ3ZQVHl0UEVzcW9pQ0hFRlVGVGtw?= =?utf-8?B?RG5sTjZnSFFhWnl5akNQeE9EQ2JXbDJYREU4MFJlQ0FXRGxoSVJaeWM2NmJQ?= =?utf-8?B?Q2xuZ3pzK2VleUVJbXdwNHFhK05ZM1lKc1U2a1FnNXorSE8waDQrTFp1WEtS?= =?utf-8?B?Y3FJcmNBTXpYM2N4RlJoOWI5UGNINlNPOEFzZDR2VzBNQktzVWRlUmErajNy?= =?utf-8?B?THQ0VVh4enFxakNlbDdYN25MTVorMUtoRmtNSVlHQWdObkFyenl1c0JENTMy?= =?utf-8?B?ZU1VRFFFamlaYkI2d20yQm1HVkZ4N1o2Wlp0RlVTVk9rcE41Mm4rbjY5bmJY?= =?utf-8?B?NGZ4RHVlcDNqNkVwQ2VObS93NDVjRzdYRVRUblQzOWVpNHlDdWVkeXZwbktJ?= =?utf-8?B?ckQrY2ZJSE1nT3lLWE1JYWt2cVNjTEpSeVMvU3Z6TmFuS09Iem5rVGFSTmwx?= =?utf-8?B?eUtDd1VvRmNVK1RpayttM2hXS3Byc0JnbFd4bW5HSjBFaGNNczRBT3RoL2V0?= =?utf-8?B?b29qU05wV3IrcHJjYzVOZlhkTEc4aGVWeTVEZU5wVnVJTjVDb1Nnbm9nSXQz?= =?utf-8?B?SzNJNU95MlRhYlYzUFdyRVptcVNZbmV5dHhtU3Foa2FCc0o1NFcwNk81ZEpU?= =?utf-8?B?ci8ycU1pa1ZESkhQbDlvVG1zQmRwbWJIVGhad05hRU1FSXRvcW9ZV2FLUGox?= =?utf-8?B?Rll4NlYrSjFmendPWWh5azRYSzk3bCthV3lHeWxYczNnSy9vYXY3YlA2YkpD?= =?utf-8?B?VFJzWVUxVStidE9mNkFPYkQwTTV0a0VBTllWUFdDS0Z2bGFsNkdmZ0dhQmpO?= =?utf-8?B?Mko1R0UvRm13RkdxdWVIaHJuQ1ZsZlZ0Q3hHbVVlNDIvWDdFWldDZUEzdllp?= =?utf-8?B?Z2ZVcm9ZTFVPaGVhOXVDTjBIZGFKM2JJN2pmZHJvZjZrdXE3UFBzcVlJdjQ1?= =?utf-8?B?bktXUVppcHU2Q0tTZk00OXNNOFZUdjFPa0hOdTd1T09tV2w5RmczemoycXZE?= =?utf-8?B?VDU0Z2w2bGhmYnBYRTYxVzZxbC9yTXR2MUN4NnV4ZkZYT0djZVBKZWFWUzg0?= =?utf-8?B?YmpmWDc0Mk1la2FIenc4NFkrT210UW9tRk9IMCtTQk52UUVlZTV5UjlsZGs0?= =?utf-8?B?ZlQyMlYvZEg3cytHL24xS3dpWU9mdFhEWUNPQnZpQzg5alV1VlVxQllaWmRo?= =?utf-8?B?V1NrcENXZ0NIckQzV1d0aVRYeVA3RW9wdmZ1dUhwRThDdWFHTFJxMzF2K1gv?= =?utf-8?B?QWZmU1dkSnE0Y3lZenNyNk5Hblk4MlloU1VZMVBvUHE0NlUra3ZsRUdOT3M2?= =?utf-8?B?Q3pmeU9pdlZadzJUS3JaQXEvblJUaUl6bnFOWEtxQTFlNHhPSFNySktqRksz?= =?utf-8?Q?bGG/kyAWVOiZ9qH1lC0tfguYNO/5Skg2?= X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:CH7PR03MB7860.namprd03.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(376014)(366016)(1800799024);DIR:OUT;SFP:1101; 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This is not really > great, as MMCFG is more flexible and doesn't require a dedicated lock, so it would > be preferable to use it whenever possible. > > Teddy Astie (2): > x86/pci: Improve pci_mmcfg_{read,write} error handling > x86/pci: Prefer using mmcfg for accessing configuration space AFAICT Linux is using the same approach as Xen to perform PCI accesses. Registers below 256 on segment 0 are accessed using the legacy method (IO ports), while the extended space is accessed using MMCFG. Do you know the reason for this? I fear there might be legacy devices/bridges (or root complexes?) where MMCFG is not working as expected? I think we need to understand why Xen (and Linux) do it this way so it can be properly justified why it's safe to switch to a different approach. Thanks, Roger.