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

[Baolu Lu]

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