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client-ip=165.204.84.17; helo=SATLEXMB04.amd.com; pr=C Received: from SATLEXMB04.amd.com (165.204.84.17) by CO1PEPF000075EF.mail.protection.outlook.com (10.167.249.38) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.20.8964.20 via Frontend Transport; Fri, 25 Jul 2025 10:29:45 +0000 Received: from [10.136.41.253] (10.180.168.240) by SATLEXMB04.amd.com (10.181.40.145) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.39; Fri, 25 Jul 2025 05:29:40 -0500 Message-ID: <90529f27-6e64-4756-9999-b572621b8d6d@amd.com> Date: Fri, 25 Jul 2025 15:59:37 +0530 Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 2/4] iommu/amd: Reuse device table for kdump To: Ashish Kalra , , , , , , CC: , , , , , , , , , , References: <0a9f79741e8a5b1619069a892bc5c22f17df1c34.1753133022.git.ashish.kalra@amd.com> Content-Language: en-US From: Sairaj Kodilkar In-Reply-To: <0a9f79741e8a5b1619069a892bc5c22f17df1c34.1753133022.git.ashish.kalra@amd.com> Content-Type: text/plain; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 25 Jul 2025 10:29:45.3763 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: bf2df71a-ba40-495c-7578-08ddcb662cd3 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: CO1PEPF000075EF.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CYXPR12MB9387 On 7/22/2025 3:23 AM, Ashish Kalra wrote: > From: Ashish Kalra > > After a panic if SNP is enabled in the previous kernel then the kdump > kernel boots with IOMMU SNP enforcement still enabled. > > IOMMU device table register is locked and exclusive to the previous > kernel. Attempts to copy old device table from the previous kernel > fails in kdump kernel as hardware ignores writes to the locked device > table base address register as per AMD IOMMU spec Section 2.12.2.1. > > This results in repeated "Completion-Wait loop timed out" errors and a > second kernel panic: "Kernel panic - not syncing: timer doesn't work > through Interrupt-remapped IO-APIC". > > Reuse device table instead of copying device table in case of kdump > boot and remove all copying device table code. > > Signed-off-by: Ashish Kalra Tested-by: Sairaj Kodilkar