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Thu, 18 Dec 2025 09:32:44 -0800 Date: Thu, 18 Dec 2025 09:32:43 -0800 From: Nicolin Chen To: Mostafa Saleh CC: , , , , , , , , , Subject: Re: [PATCH rc v4 3/4] iommu/arm-smmu-v3: Mark STE EATS safe when computing the update sequence Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-NV-OnPremToCloud: ExternallySecured X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CY4PEPF0000E9D8:EE_|IA1PR12MB7661:EE_ X-MS-Office365-Filtering-Correlation-Id: b7825688-bc31-4d30-7886-08de3e5b84ce X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|36860700013|376014|82310400026|1800799024; X-Microsoft-Antispam-Message-Info: =?utf-8?B?V0YzeFplSkFCdkt6U1ZJTFBYR0MvczEwL1lxbVY2RS9ORFVKZEJkUzZ1dVdy?= =?utf-8?B?aGNYM2tDMElPVm1WQUVpWWNyYjQxSEV1MmJvMGZQaEMrbDhJcys0eC9ab2ZP?= =?utf-8?B?S0NiRFpKOXVIUnFISUJFRHhCUU04a0xUbnFaOEFBeDloNTRxWDZGV3VhTjZ0?= =?utf-8?B?WjFIQ1haZGRUaERFd2tCcmJ2WHRPQXJBR3FEa250N1RVWlAvRlJSeUt1UFZs?= =?utf-8?B?NktjL3ZSTkU1TGpDV3Q4dmZhUmd2UXVRTkRFWGpDenBPN1JDbmNVeWxoU3Vl?= =?utf-8?B?dTdUV2JQaC9HUzIzUkxHTFk1ZGgxQ3BFUWc3UHpNQ0c3aHRQKzdDdkNnY3NJ?= =?utf-8?B?QUNlSk14bXoxWlJiS1U3WGhrcFZCRHB2ellmWXNlNVZVQVdaOEltUXM0ZTZh?= =?utf-8?B?RmJYSXN5cWNrcXNUQWhBRHdWaHk1bklvMWdCZkZSQm5aL1lwWk9CSWdMS3N0?= =?utf-8?B?UGc4WHZib2VXTGx5cGlWRDZFT3d2L3YwUEsyMEhFVmtHODV2Vko4M25NeVRq?= =?utf-8?B?STJFcXY2SzA4VFkwMXpOWFdUNVdobjh6bWdKNEVMZzJwNUhMTTlVS29HcGQv?= =?utf-8?B?eEkvNUt2RXBQN3p0QXVuMzZhZjlYMTRIeVQrWjl2WDVic04wS3Uva0tNamhY?= =?utf-8?B?TkFaV09mazY0NUE4WUlGQmUvMjZ0TFg4SVJQT0txdndKTjQxdnJFdTYzR2hv?= =?utf-8?B?L3VPLzVabXNuWDY4VVZ2WDhCdVpSK0VIR2dBam84ajZGM25odHJnZUNuOWxi?= =?utf-8?B?VW94M3dEYmxDdEY3VkR3Tms3T2wrSEg0VkFaOUU2MDh0T2k2dlRkMk1aRW1z?= =?utf-8?B?SG5kRS8ydUxieWo3UEtoQWRCMWtjYTRCZkNmQytybjh1elpPUy92c0IrN0t5?= =?utf-8?B?aUNJUitPVWl3bTJSK0Z3SXplKzJJaWdhRzE1Nm1icmFvVE5ML3loNTNVT2Ji?= =?utf-8?B?NCt4NGpHaFJpRjdGRXVHaldUZ0JJUGlKcndNeHU5UWNXUzZjUFE4V2YzSWJD?= =?utf-8?B?TmliNlErcmNOeUJEUDBzNWpOM1R5TllEb1JhbmN1TGt4VWs0YlRZRTMrTHJ5?= =?utf-8?B?dW5zYmc4YWR0c0tlZnQ1RVpIV2t4NTZKbjc1OFVWS1ZrMkdNR0hFYWVxb0pH?= =?utf-8?B?Zm50R3d3VU9IcllmcTYvbkRQWThhc2YrMFQ3a2swR3Y0VzgzSlF1MzF6RVdz?= =?utf-8?B?T0U1Wjh2c0pNaWNKYitRZmxjclQwTk1leTQyYXhseDdVd3hFZ044UHl1d1JU?= =?utf-8?B?azkwd2JCTFhEUHJGYk82QkF1cjZ4R0tFUU4zbDZMVVI3MmFPNm82NE9GZDhz?= =?utf-8?B?M1RWUEZNa2V2ODhUSzJzY1djSHhaVFdOQjIyWThzM3dSQk9ZWUdDZmxHSGRF?= =?utf-8?B?ejQ3aGZBaDlHQkpxV3R1ZjIwbnJMU3Q2NVE2MUxEcFY1Rlh4dXN4RWkvTzcw?= =?utf-8?B?ZGZENG5vWXZTT2VFbTYvZ01BRi9SOHVNbEdMZWFwSTd3RVZoOGQvZFcyUFB6?= =?utf-8?B?YzFzZW1jV3UwZmVxOFFFM2FDREV0YVBISm83eklMaFVYK1JkNUlERi9jMjVr?= =?utf-8?B?MFJ2U1g2eE5JRkc2YmhKeU5aVWNDS29XVFRjN0M0b1hzellwOEcvR0xpN2J6?= =?utf-8?B?UEV3TWFzaEZ0WFU5TGw3UUlrcURWcDZuK2I0ckc3MXBaTUhRamc5OElUaFlG?= =?utf-8?B?MEUvb0FVNk9KSjNTSTNTRmhPRmJQSHZIMUwxdTZHSUt3amtzamJ1c1NTRkls?= =?utf-8?B?OGJJS1JYWTZpeFFEVWUwL0Zydkd1ZWVIYTNITkFGd2NBZGx2QmQ2NkQyemJV?= =?utf-8?B?bVlqQUppMzNWMTBOSEFsaUxHSmlDQk9CODIzZEIvbEcveFdwM2xSVHlsU0Rl?= =?utf-8?B?RVhDWmxPdzJGejdpeWk1OE1ReGs2OGFTSTZVaTJGdmxrZ3NhQ0NDWFc5NWt2?= =?utf-8?B?YW05NTgvclY0bkxxTXpJTjJDdmlSVHdva1JOdnNjN0VucGxIUDVuQjF0eWlq?= =?utf-8?B?ZlVHTWpDYVBxTms4aERYZkkyZktMMUh5R2l4YXdBaEwra0REWWs5NHZRMmQw?= =?utf-8?B?Tm13bTZNbkZqZ3FXbmQ3Y0ZUY1Zpbnk3TVM2Q0oxeWJiQ2gra2QxQ0Jwc25O?= =?utf-8?Q?G61U=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)(376014)(82310400026)(1800799024);DIR:OUT;SFP:1101; X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 Dec 2025 17:33:12.3165 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: b7825688-bc31-4d30-7886-08de3e5b84ce 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: CY4PEPF0000E9D8.namprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA1PR12MB7661 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251218_093325_602644_035E1D06 X-CRM114-Status: GOOD ( 32.60 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Dec 18, 2025 at 04:42:40PM +0000, Mostafa Saleh wrote: > On Tue, Dec 16, 2025 at 08:26:01PM -0800, Nicolin Chen wrote: > > From: Jason Gunthorpe > > > > If a VM wants to toggle EATS off at the same time as changing the CFG, the > > hypervisor will see EATS change to 0 and insert a V=0 breaking update into > > the STE even though the VM did not ask for that. > > > > In bare metal, EATS is ignored by CFG=ABORT/BYPASS, which is why this does > > not cause a problem until we have nested where CFG is always a variation of > > S2 trans that does use EATS. > > > > Relax the rules for EATS sequencing, we don't need it to be exact because > > the enclosing code will always disable ATS at the PCI device if we are > > changing EATS. This ensures there are no ATS transactions that can race > > with an EATS change so we don't need to carefully sequence these bits. > > > > Fixes: 1e8be08d1c91 ("iommu/arm-smmu-v3: Support IOMMU_DOMAIN_NESTED") > > Cc: stable@vger.kernel.org > > Signed-off-by: Jason Gunthorpe > > Reviewed-by: Shuai Xue > > Signed-off-by: Nicolin Chen > > --- > > drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 9 +++++++++ > > 1 file changed, 9 insertions(+) > > > > 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 12a9669bcc83..a3b29ad20a82 100644 > > --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > > +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c > > @@ -1095,6 +1095,15 @@ void arm_smmu_get_ste_update_safe(__le64 *safe_bits) > > * fault records even when MEV == 0. > > */ > > safe_bits[1] |= cpu_to_le64(STRTAB_STE_1_MEV); > > + > > + /* > > + * EATS is used to reject and control the ATS behavior of the device. If > > + * we are changing it away from 0 then we already trust the device to > > + * use ATS properly and we have sequenced the device's ATS enable in PCI > > + * config space to prevent it from issuing ATS while we are changing > > + * EATS. > > + */ > > I am not sure about this one, Is it only about trusting the device? > > I’d be worried about cases where we switch domains, that means that > briefly the HW observers EATS=1 while it was not intended, especially > that EATS is in a different DWORD from S2TTB and CDptr. With all the > IOMMUFD/VFIO stuff it makes it harder to reason about. But I can’t > come up with an example to break this. Hmm.. I think the last line that driver controls pci_enable/disable_ats() should justify the whole thing? Are you worried about device still doing ATS after pci_disable_ats()? Thanks Nicolin