Re: [bug report] iommu/arm-smmu-v3: Event cannot be printed in some scenarios

[Baolu Lu <baolu.lu@linux.intel.com>]

On 2024/8/6 23:58, Pranjal Shrivastava wrote:
> On Tue, Aug 06, 2024 at 09:49:43AM -0300, Jason Gunthorpe wrote:
>> On Mon, Aug 05, 2024 at 03:32:50PM +0000, Pranjal Shrivastava wrote:
>>> Here's the updated diff:
>>> 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 a31460f9f3d4..ed2b106e02dd 100644
>>> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
>>> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
>>> @@ -1777,7 +1777,7 @@ static int arm_smmu_handle_evt(struct arm_smmu_device *smmu, u64 *evt)
>>>   		goto out_unlock;
>>>   	}
>>>   
>>> -	iommu_report_device_fault(master->dev, &fault_evt);
>>> +	ret = iommu_report_device_fault(master->dev, &fault_evt);
>>>   out_unlock:
>>>   	mutex_unlock(&smmu->streams_mutex);
>>>   	return ret;
>>> diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
>>> index 0e3a9b38bef2..7684e7562584 100644
>>> --- a/drivers/iommu/intel/svm.c
>>> +++ b/drivers/iommu/intel/svm.c
>>> @@ -532,6 +532,9 @@ void intel_svm_page_response(struct device *dev, struct iopf_fault *evt,
>>>   	bool last_page;
>>>   	u16 sid;
>>>   
>>> +	if (!evt)
>>> +		return;
>>> +
>> I'm not sure this make sense??
>>
>> The point of this path is for the driver to retire the fault with a
>> failure. This prevents that from happing on Intel and we are back to
>> loosing track of a fault.
>>
>> All calls to iommu_report_device_fault() must result in
>> page_response() properly retiring whatever the event was.
>>
>>> +static void iopf_error_response(struct device *dev, struct iommu_fault *fault)
>>> +{
>>> +	const struct iommu_ops *ops = dev_iommu_ops(dev);
>>> +	struct iommu_page_response resp = {
>>> +		.pasid = fault->prm.pasid,
>>> +		.grpid = fault->prm.grpid,
>>> +		.code = IOMMU_PAGE_RESP_INVALID
>>> +	};
>>> +
>>> +	ops->page_response(dev, NULL, &resp);
>>> +}
>> The issue originates here, why is this NULL?
>>
>> void iommu_report_device_fault(struct device *dev, struct iopf_fault *evt)
>> {
>>
>> The caller has an evt? I think we should pass it down.
> Hmm, I agree, I don't see `iommu_report_device_fault` be called anywhere
> with a NULL evt. Hence, it does make sense to pass the evt down and
> ensure we don't lose track of the event.
> 
> I'm assuming that we retired the if (!evt) check from intel->page
> response since we didn't have any callers of intel->page_response
> with a NULL evt. (Atleast, for now, I don't see that happen).
> 
> Lu, Will -- Any additional comments/suggestions for this?

No. If evt is passed down in the above code, there is no need to add
such check anymore.

Thanks,
baolu