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Thu, 21 Nov 2024 21:05:24 +0000 (GMT) Received: from nasanex01c.na.qualcomm.com (nasanex01c.na.qualcomm.com [10.45.79.139]) by NASANPPMTA02.qualcomm.com (8.18.1.2/8.18.1.2) with ESMTPS id 4ALL5MQm005703 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 21 Nov 2024 21:05:22 GMT Received: from [10.216.44.227] (10.80.80.8) by nasanex01c.na.qualcomm.com (10.45.79.139) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.9; Thu, 21 Nov 2024 13:05:17 -0800 Message-ID: <124a3aba-138c-41e8-abe0-e6b75f0d8aee@quicinc.com> Date: Fri, 22 Nov 2024 02:35:13 +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 v2] iommu/arm-smmu: Defer probe of clients after smmu device bound To: Robin Murphy , Will Deacon CC: , , , , , , , , , , , , , Prakash Gupta References: <20241004090428.2035-1-quic_pbrahma@quicinc.com> <173021496151.4097715.14758035881649445798.b4-ty@kernel.org> <0952ca36-c5d9-462a-ab7b-b97154c56919@arm.com> <1d3dcd91-d246-4db3-9717-9edfe405f431@quicinc.com> <57477eba-ef6a-454b-85d1-d0244f6116d1@arm.com> Content-Language: en-US From: Pratyush Brahma In-Reply-To: <57477eba-ef6a-454b-85d1-d0244f6116d1@arm.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: nasanex01b.na.qualcomm.com (10.46.141.250) To nasanex01c.na.qualcomm.com (10.45.79.139) X-QCInternal: smtphost X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=5800 signatures=585085 X-Proofpoint-GUID: MawJVwAjKTK0gsoaaSF6X6yYMat8Kf2R X-Proofpoint-ORIG-GUID: MawJVwAjKTK0gsoaaSF6X6yYMat8Kf2R X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1039,Hydra:6.0.680,FMLib:17.12.60.29 definitions=2024-09-06_09,2024-09-06_01,2024-09-02_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 lowpriorityscore=0 clxscore=1011 bulkscore=0 adultscore=0 suspectscore=0 spamscore=0 malwarescore=0 mlxscore=0 mlxlogscore=999 phishscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2409260000 definitions=main-2411210157 On 11/21/2024 8:19 PM, Robin Murphy wrote: > On 2024-11-19 7:10 pm, Pratyush Brahma wrote: >> >> On 11/7/2024 8:31 PM, Robin Murphy wrote: >>> On 29/10/2024 4:15 pm, Will Deacon wrote: >>>> On Fri, 04 Oct 2024 14:34:28 +0530, Pratyush Brahma wrote: >>>>> Null pointer dereference occurs due to a race between smmu >>>>> driver probe and client driver probe, when of_dma_configure() >>>>> for client is called after the iommu_device_register() for smmu >>>>> driver >>>>> probe has executed but before the driver_bound() for smmu driver >>>>> has been called. >>>>> >>>>> Following is how the race occurs: >>>>> >>>>> [...] >>>> >>>> Applied to will (for-joerg/arm-smmu/updates), thanks! >>>> >>>> [1/1] iommu/arm-smmu: Defer probe of clients after smmu device bound >>>>        https://git.kernel.org/will/c/229e6ee43d2a >>> >>> I've finally got to the point of proving to myself that this isn't the >>> right fix, since once we do get __iommu_probe_device() working properly >>> in the correct order, iommu_device_register() then runs into the same >>> condition itself. Diff below should make this issue go away - I'll >>> write >>> up proper patches once I've tested it a little more. >>> >>> Thanks, >>> Robin. >>> >>> ----->8----- >>> 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 737c5b882355..b7dcb1494aa4 100644 >>> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c >>> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c >>> @@ -3171,8 +3171,8 @@ static struct platform_driver arm_smmu_driver; >>>  static >>>  struct arm_smmu_device *arm_smmu_get_by_fwnode(struct fwnode_handle >>> *fwnode) >>>  { >>> -    struct device *dev = >>> driver_find_device_by_fwnode(&arm_smmu_driver.driver, >>> -                              fwnode); >>> +    struct device *dev = >>> bus_find_device_by_fwnode(&platform_bus_type, fwnode); >>> +      put_device(dev); >>>      return dev ? dev_get_drvdata(dev) : NULL; >>>  } >>> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c b/drivers/iommu/ >>> arm/arm-smmu/arm-smmu.c >>> index 8321962b3714..aba315aa6848 100644 >>> --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c >>> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c >>> @@ -1411,8 +1411,8 @@ static bool arm_smmu_capable(struct device >>> *dev, enum iommu_cap cap) >>>  static >>>  struct arm_smmu_device *arm_smmu_get_by_fwnode(struct fwnode_handle >>> *fwnode) >>>  { >>> -    struct device *dev = >>> driver_find_device_by_fwnode(&arm_smmu_driver.driver, >>> -                              fwnode); >>> +    struct device *dev = >>> bus_find_device_by_fwnode(&platform_bus_type, fwnode); >> I think it would still follow this path: >> >> bus_find_device_by_fwnode() -> bus_find_device() -> next_device() >> >> next_device() would always return null until the driver is bound to >> the device which > > No, this is traversing the bus list, *not* the driver list, that's the > whole point. The SMMU device must exist on the platform bus before the > driver can bind, since the bus is responsible for matching the driver > in the first place. Ah I see. Thanks for the explanation. That makes sense. > >> happens much later in really_probe() after the >> iommu_device_register() would be called >> even as per this patch. That way the race would still occur, wouldn't >> it? >> Can you please help me understand what I may be missing here? >> Are you saying that these additional patches are required along with >> the fix I've >> posted? > > I'm saying my change makes there be no race, i.e. the "if (!smmu)" > case can never be true, and so no longer needs working around. Got it. Thanks. > > Thanks, > Robin. > >>> + >>>      put_device(dev); >>>      return dev ? dev_get_drvdata(dev) : NULL; >>>  } >>> @@ -2232,21 +2232,6 @@ static int arm_smmu_device_probe(struct >>> platform_device *pdev) >>>                      i, irq); >>>      } >>> >>> -    err = iommu_device_sysfs_add(&smmu->iommu, smmu->dev, NULL, >>> -                     "smmu.%pa", &smmu->ioaddr); >>> -    if (err) { >>> -        dev_err(dev, "Failed to register iommu in sysfs\n"); >>> -        return err; >>> -    } >>> - >>> -    err = iommu_device_register(&smmu->iommu, &arm_smmu_ops, >>> -                    using_legacy_binding ? NULL : dev); >>> -    if (err) { >>> -        dev_err(dev, "Failed to register iommu\n"); >>> -        iommu_device_sysfs_remove(&smmu->iommu); >>> -        return err; >>> -    } >>> - >>>      platform_set_drvdata(pdev, smmu); >>> >>>      /* Check for RMRs and install bypass SMRs if any */ >>> @@ -2255,6 +2240,18 @@ static int arm_smmu_device_probe(struct >>> platform_device *pdev) >>>      arm_smmu_device_reset(smmu); >>>      arm_smmu_test_smr_masks(smmu); >>> >>> +    err = iommu_device_sysfs_add(&smmu->iommu, smmu->dev, NULL, >>> +                     "smmu.%pa", &smmu->ioaddr); >>> +    if (err) >>> +        return dev_err_probe(dev, err, "Failed to register iommu in >>> sysfs\n"); >>> + >>> +    err = iommu_device_register(&smmu->iommu, &arm_smmu_ops, >>> +                    using_legacy_binding ? NULL : dev); >>> +    if (err) { >>> +        iommu_device_sysfs_remove(&smmu->iommu); >>> +        return dev_err_probe(dev, err, "Failed to register iommu\n"); >>> +    } >>> + >>>      /* >>>       * We want to avoid touching dev->power.lock in fastpaths unless >>>       * it's really going to do something useful - pm_runtime_enabled() >> > -- Thanks and Regards Pratyush Brahma