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Mon, 12 Jan 2026 12:20:32 -0800 From: Nicolin Chen To: CC: , , , , , , , , , Subject: [PATCH rc v6 2/4] iommu/arm-smmu-v3: Mark STE MEV safe when computing the update sequence Date: Mon, 12 Jan 2026 12:20:15 -0800 Message-ID: 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: quoted-printable X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BN3PEPF0000B071:EE_|MW4PR12MB6900:EE_ X-MS-Office365-Filtering-Correlation-Id: 55a3890d-660d-4a7e-08cd-08de521815df X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|36860700013|82310400026|1800799024|376014; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?WZtck/FjalrY55J0VREGIrngHR0jBot5TRXzHmZdOscxUrnaNkhhKmaVgVEk?= =?us-ascii?Q?EHxYUYClk1Pj20SPxhhzEprfgqgJ+0LDDZhRdKPTss791qmMD8mFkc06HZS5?= =?us-ascii?Q?mFPOYQrgM9XbK4IPFV4xtIZZa+CM9k/STHRbwfBiifqY6SZzLHzKXy0zhf3P?= =?us-ascii?Q?63rf5tAi9+uHqhAXVzv1U7cfoQkuteeU0RadS+Zg83aotuGTbpMrnn7QLG+8?= =?us-ascii?Q?UPJl/iDE8UG6PAb6uNVsGi28jHt5cQwD1feKMTScFsvqpl46P4rhtZL6hTjD?= =?us-ascii?Q?UGQwJKim7LGBhX9QXdi00+mQ5T/VCoRO9Pnp4/ujrt8E+TEQXXsLmShIybLi?= =?us-ascii?Q?4EuU3VlXXBrg9L27o/Tzj5Jy5W+zjZP4vVQwQB6+JdC2WnyhszzW6ewbHDz/?= =?us-ascii?Q?lSVq26+TrUSau7FpU0O0gBehMIN5k/WV3PJYbdHn8dEoJrCyWX/5RJYkvLP7?= =?us-ascii?Q?DDL6CVQGAUeC3towBPZ99eOvZAiEHH+/5hoopPFHqZc47w3B9So2e+6hC+CJ?= =?us-ascii?Q?iFXGlZDFjpkrsIyHt8py2wOOMgwa6Hwpsgaidj9K1oMunPFyAsqWXHIWRmQH?= =?us-ascii?Q?EauzyZ7loyn22bPnLoYtJhu6dPOVYoWNgPommC6VrAaWvoKdZY9GLt+kJMqE?= =?us-ascii?Q?amBZRJU1TKeuOTE9wPKhtE0YAnoBtN/xR8zEIjeoTpKmUhd3tDeWK5S1tNkr?= =?us-ascii?Q?j/x+rxiTHmswyJeaeN6aDnaJalMg/jqRZdkgusJpbWySqSl1aw4Mx4MrE5lI?= =?us-ascii?Q?3aeLDJBSQtejc7gXFmPujQ7+XoBvBE78GBDjHRwtpUNQL+i3auHKqm6tXAx5?= =?us-ascii?Q?pCxJ1qt233lFqE7Sc8D18r8ug0nWbCEAhphpx2Lq/Ho7lFRJkBbW4sizpMQm?= =?us-ascii?Q?nxVc5JcUslh6BGgytZO8/9sPnjaFzHLW4y3ewZAA5ZUm2znDp/WPrQpwJOvk?= =?us-ascii?Q?mTh2cHnhLfq6TmUEVAhf1Xo1fCDnxGWLuPrV+/VsqL3PhCCofgGUTXfOCYXN?= =?us-ascii?Q?+ARKfMa2o9OWQUySb7U/qj6eo+x7X9Wy2wQqnLLgmCzSt1ASnauXoEp+xbVx?= =?us-ascii?Q?Se8AP2GpdAWzRETi3t5AUSCwbRL4EFgNdIX3RuNJy7DB9UGHTkkuCgm80XHE?= =?us-ascii?Q?L13izmuk2Y8il4dBws7Jv+TN0PRfKrxdc+dM5HUBPq4T//7k5Gy4g78tMaxv?= =?us-ascii?Q?mLNruHDdYf1aonA4RndhSoWS8Uitws30Jg++VxtHcGQzgZMGlZ1gUVJr5cfG?= =?us-ascii?Q?Xd02ItLWY65zjSvcQGHrHnsYRCAoT4iXLw8RFL0mFCQs+/b6Gy2Awg2ZfsGB?= =?us-ascii?Q?WHAVp8q16841YP2mj4X9Cfy+NkQgGTvcD9ly2e4eSf0E700Hjvdoh7tgg0p1?= =?us-ascii?Q?Uz6NiF3chkiKfEg/6pAv2nOcKmbfqqu9y2V1wVDnZTVY6pHBazl9hWUoE5Sb?= =?us-ascii?Q?p5hchosISTVqIEF/khUHcxac8HSWJHRC1x44We4gJRY/7rcy8MiT6wQDGVAb?= =?us-ascii?Q?bCLjbUBTJA8WbrAWiABRLZ6CD7l2d3kRzvCqXjwM+/DYnsWLyszC2nTDbeiG?= =?us-ascii?Q?ekIaRRUgFZ9AVJd2Zzs=3D?= X-Forefront-Antispam-Report: CIP:216.228.117.160;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:mail.nvidia.com;PTR:dc6edge1.nvidia.com;CAT:NONE;SFS:(13230040)(36860700013)(82310400026)(1800799024)(376014);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 12 Jan 2026 20:20:53.0751 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 55a3890d-660d-4a7e-08cd-08de521815df X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.117.160];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: BN3PEPF0000B071.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW4PR12MB6900 Content-Type: text/plain; charset="utf-8" From: Jason Gunthorpe Nested CD tables set the MEV bit to try to reduce multi-fault spamming on the hypervisor. Since MEV is in STE word 1 this causes a breaking update sequence that is not required and impacts real workloads. For the purposes of STE updates the value of MEV doesn't matter, if it is set/cleared early or late it just results in a change to the fault reports that must be supported by the kernel anyhow. The spec says: Note: Software must expect, and be able to deal with, coalesced fault records even when MEV =3D=3D 0. So mark STE MEV safe when computing the update sequence, to avoid creating a breaking update. Fixes: da0c56520e88 ("iommu/arm-smmu-v3: Set MEV bit in nested STE for DoS = mitigations") Cc: stable@vger.kernel.org Signed-off-by: Jason Gunthorpe Reviewed-by: Shuai Xue Reviewed-by: Mostafa Saleh Signed-off-by: Nicolin Chen Reviewed-by: Pranjal Shrivastava --- drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/ar= m/arm-smmu-v3/arm-smmu-v3.c index 390446d259ab..ccd6357fa5a8 100644 --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c @@ -1086,6 +1086,16 @@ VISIBLE_IF_KUNIT void arm_smmu_get_ste_update_safe(const __le64 *cur, const __le64 *target, __le64 *safe_bits) { + /* + * MEV does not meaningfully impact the operation of the HW, it only + * changes how many fault events are generated, thus we can relax it + * when computing the ordering. The spec notes the device can act like + * MEV=3D1 anyhow: + * + * Note: Software must expect, and be able to deal with, coalesced + * fault records even when MEV =3D=3D 0. + */ + safe_bits[1] |=3D cpu_to_le64(STRTAB_STE_1_MEV); } EXPORT_SYMBOL_IF_KUNIT(arm_smmu_get_ste_update_safe); =20 --=20 2.43.0