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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 CO1PEPF000075F0.mail.protection.outlook.com (10.167.249.39) 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 10:29:00 +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 05:28:55 -0500 Message-ID: <4134f54f-9b01-47fc-be40-6829aeae1fcd@amd.com> Date: Fri, 25 Jul 2025 15:58:52 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 1/4] iommu/amd: Add support to remap/unmap IOMMU buffers for kdump To: Ashish Kalra , , , , , , CC: , , , , , , , , , , References: <6a48567cd99a0ef915862b3c6590d1415d287870.1753133022.git.ashish.kalra@amd.com> Content-Language: en-US From: Sairaj Kodilkar In-Reply-To: <6a48567cd99a0ef915862b3c6590d1415d287870.1753133022.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 10:29:00.0846 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 407b3152-fbda-4f9a-52ff-08ddcb6611cc 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: CO1PEPF000075F0.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW4PR12MB7165 On 7/22/2025 3:22 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 completion wait buffers (CWBs), command buffers and event buffer > registers remain locked and exclusive to the previous kernel. Attempts > to allocate and use new buffers in the kdump kernel fail, as hardware > ignores writes to the locked MMIO registers 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" > > The list of MMIO registers locked and which ignore writes after failed > SNP shutdown are mentioned in the AMD IOMMU specifications below: > > Section 2.12.2.1. > https://docs.amd.com/v/u/en-US/48882_3.10_PUB > > Reuse the pages of the previous kernel for completion wait buffers, > command buffers, event buffers and memremap them during kdump boot > and essentially work with an already enabled IOMMU configuration and > re-using the previous kernel’s data structures. > > Reusing of command buffers and event buffers is now done for kdump boot > irrespective of SNP being enabled during kdump. > > Re-use of completion wait buffers is only done when SNP is enabled as > the exclusion base register is used for the completion wait buffer > (CWB) address only when SNP is enabled. > > Signed-off-by: Ashish Kalra Tested-by: Sairaj Kodilkar