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Date: Wed, 11 Mar 2026 11:15:18 +0100 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: Julian Vetter Cc: xen-devel@lists.xenproject.org, Jan Beulich , Andrew Cooper , Anthony PERARD , Michal Orzel , Stefano Stabellini , Juergen Gross , Julien Grall Subject: Re: [PATCH v3 2/7] x86/msi: Define extended destination ID masks and IO-APIC RTE fields Message-ID: References: <20260309123055.880050-1-julian.vetter@vates.tech> <20260309123055.880050-2-julian.vetter@vates.tech> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20260309123055.880050-2-julian.vetter@vates.tech> X-ClientProxiedBy: MR1P264CA0049.FRAP264.PROD.OUTLOOK.COM (2603:10a6:501:3e::15) To CH7PR03MB7860.namprd03.prod.outlook.com (2603:10b6:610:24e::14) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CH7PR03MB7860:EE_|DS1PR03MB7967:EE_ X-MS-Office365-Filtering-Correlation-Id: 3919a747-3908-462a-4603-08de7f571a89 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|376014|56012099003|18002099003|22082099003; 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However there's an unofficial extension to the MSI messages format that re-use some reserved bits to expand the destination field from 8 to 15 bits." Or similar. > 8-bit range provided by the standard MSI address and IO-APIC RTE fields. > The Intel spec allows bits 11:5 of the MSI address and bits 55:49 of the > IO-APIC RTE to carry the high 7 bits of the destination ID when the > platform advertises support, expanding the range to 15 bits total. Hm, I'm really unsure the Intel spec allows for any of this. This is something that has been done on the side, re-using bits marked as reserved in the spec. Thanks, Roger.