Re: [PATCH v2 08/12] iommu: Prepare for separating SVA and IOPF

[Baolu Lu]

On 2023/8/3 16:16, Tian, Kevin wrote:
> > From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > Sent: Thursday, July 27, 2023 1:49 PM
> >
> > @@ -82,7 +82,7 @@ static void iopf_handler(struct work_struct *work)
> >   	if (!domain || !domain->iopf_handler)
> >   		status = IOMMU_PAGE_RESP_INVALID;
> >
> > -	list_for_each_entry_safe(iopf, next, &group->faults, list) {
> > +	list_for_each_entry(iopf, &group->faults, list) {
> >   		/*
> >   		 * For the moment, errors are sticky: don't handle
> > subsequent
> >   		 * faults in the group if there is an error.
> > @@ -90,14 +90,20 @@ static void iopf_handler(struct work_struct *work)
> >   		if (status == IOMMU_PAGE_RESP_SUCCESS)
> >   			status = domain->iopf_handler(&iopf->fault,
> >   						      domain->fault_data);
> > -
> > -		if (!(iopf->fault.prm.flags &
> > -		      IOMMU_FAULT_PAGE_REQUEST_LAST_PAGE))
> > -			kfree(iopf);
> >   	}
> >
> >   	iopf_complete_group(group->dev, &group->last_fault, status);
> > -	kfree(group);
> > +	iopf_free_group(group);
> > +}
>
> this is perf-critical path. It's not good to traverse the list twice.

Freeing the fault group is not critical anymore, right?

> > +
> > +static int iopf_queue_work(struct iopf_group *group, work_func_t func)
> > +{
> > +	struct iopf_device_param *iopf_param = group->dev->iommu-
> > > iopf_param;
> > +
> > +	INIT_WORK(&group->work, func);
> > +	queue_work(iopf_param->queue->wq, &group->work);
> > +
> > +	return 0;
> >   }
>
> Is there plan to introduce further error in the future? otherwise this should
> be void.

queue_work() return true or false. I should check and return the value.

> btw the work queue is only for sva. If there is no other caller this can be
> just kept in iommu-sva.c. No need to create a helper.

The definition of struct iopf_device_param is in this file. So I added a
helper to avoid making iopf_device_param visible globally.

> > @@ -199,8 +204,11 @@ int iommu_queue_iopf(struct iommu_fault *fault,
> > struct device *dev)
> >   			list_move(&iopf->list, &group->faults);
> >   	}
> >
> > -	queue_work(iopf_param->queue->wq, &group->work);
> > -	return 0;
> > +	ret = iopf_queue_work(group, iopf_handler);
> > +	if (ret)
> > +		iopf_free_group(group);
> > +
> > +	return ret;
>
> Here we can document that the iopf handler (in patch10) should free the
> group, allowing the optimization inside the handler.

Yeah!

Best regards,
baolu