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Sun, 30 Aug 2026 16:18:41 -0700 From: Nicolin Chen To: , , CC: , , , , , , , , Subject: [PATCH v10 12/13] iommu/arm-smmu-v3: Skip RMR bypass for kdump adoption Date: Sun, 30 Aug 2026 16:18:13 -0700 Message-ID: <89285912833ba2aea8e43d10d66f0e7e01e1c256.1788130528.git.nicolinc@nvidia.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DS3PEPF0000C37D:EE_|DS0PR12MB7725:EE_ X-MS-Office365-Filtering-Correlation-Id: 742db65c-0e2e-42a7-ced0-08df06ed0d57 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|82310400026|36860700016|30052699003|23010399003|7416014|376014|6133799003|22082099003|18002099003|56012099006|11063799006|10067099003; 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A normal boot switches the driver to a fresh stream table whose initial STEs abort, so those RMR SIDs need bypass entries before it becomes live. This preserves firmware/guest-owned traffic, including vSMMU guest MSI cases built around RMR-described SIDs. ARM_SMMU_OPT_KDUMP_ADOPT is the opposite case: the driver keeps SMMUEN set and adopts the crashed kernel's stream table, so RMR SIDs already have the only translation state known to be safe for active in-flight DMA. Replacing an adopted STE with bypass can turn translated DMA into physical DMA, then point it at the wrong memory. arm_smmu_make_bypass_ste() also rewrites the STE in place after clearing it first. While the table is live, a concurrent hardware STE fetch can observe V=0 or mixed old/new state. Leaving the adopted STE unmodified keeps the kdump kernel using the crashed kernel's translation. That gives the endpoint driver a chance to probe and quiesce the device. If the old STE was already abort or invalid, installing bypass would create new DMA permission; leaving it alone is a safer failure mode. Later domain setup still gets the RMR direct mappings through the reserved-region path. Reviewed-by: Pranjal Shrivastava Reviewed-by: Jason Gunthorpe Assisted-by: Codex:gpt-5.5 Signed-off-by: Nicolin Chen --- drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c index 0fb8c60526699..525cdc2e7d495 100644 --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c @@ -5536,6 +5536,14 @@ static void arm_smmu_rmr_install_bypass_ste(struct arm_smmu_device *smmu) struct list_head rmr_list; struct iommu_resv_region *e; + /* + * Kdump adoption keeps the crashed kernel's table live. Rewriting the + * adopted STE here could expose an in-flight fetch to a transient V=0 + * entry, or change Cfg=translate to Cfg=bypass. Must skip here. + */ + if (smmu->options & ARM_SMMU_OPT_KDUMP_ADOPT) + return; + INIT_LIST_HEAD(&rmr_list); iort_get_rmr_sids(dev_fwnode(smmu->dev), &rmr_list); @@ -5552,10 +5560,7 @@ static void arm_smmu_rmr_install_bypass_ste(struct arm_smmu_device *smmu) continue; } - /* - * STE table is not programmed to HW, see - * arm_smmu_initial_bypass_stes() - */ + /* The fresh stream table is not yet live. */ arm_smmu_make_bypass_ste(smmu, arm_smmu_get_step_for_sid(smmu, rmr->sids[i])); } -- 2.43.0