Re: [PATCH RFC 09/11] iommu: Add iommu_get_domain_for_dev_pasid()

[Lu Baolu]

On 2022/3/21 20:40, Jason Gunthorpe wrote:
> On Sun, Mar 20, 2022 at 02:40:28PM +0800, Lu Baolu wrote:
> > @@ -3098,7 +3101,16 @@ int iommu_attach_device_pasid(struct iommu_domain *domain,
> >   	if (iommu_group_device_count(group) != 1)
> >   		goto out_unlock;
> >   
> > +	xa_lock(&group->pasid_array);
> > +	curr = __xa_cmpxchg(&group->pasid_array, pasid, NULL,
> > +			    domain, GFP_KERNEL);
> > +	xa_unlock(&group->pasid_array);
> > +	if (curr)
>
> curr can be an xa_err that should be propogated.

Yes, should check xa_err().

> > +		goto out_unlock;
> > +
> >   	ret = domain->ops->attach_dev_pasid(domain, dev, pasid);
> > +	if (ret)
> > +		xa_erase(&group->pasid_array, pasid);
> >   
> >   out_unlock:
> >   	mutex_unlock(&group->mutex);
> > @@ -3118,6 +3130,25 @@ void iommu_detach_device_pasid(struct iommu_domain *domain,
> >   
> >   	mutex_lock(&group->mutex);
> >   	domain->ops->detach_dev_pasid(domain, dev, pasid);
> > +	xa_erase(&group->pasid_array, pasid);
> > +	mutex_unlock(&group->mutex);
> > +	iommu_group_put(group);
> > +}
> > +
> > +struct iommu_domain *
> > +iommu_get_domain_for_dev_pasid(struct device *dev, ioasid_t pasid)
> > +{
> > +	struct iommu_domain *domain;
> > +	struct iommu_group *group;
> > +
> > +	group = iommu_group_get(dev);
> > +	if (!group)
> > +		return NULL;
> > +
> > +	mutex_lock(&group->mutex);
> > +	domain = xa_load(&group->pasid_array, pasid);
> >   	mutex_unlock(&group->mutex);
> >   	iommu_group_put(group);
>
> This whole API seems sketchy - what is the lifecycle of the returned
> iommu_domain and what prevents it from being concurrently freed after
> unlocking?

Agreed. The domain could be used in page fault handling thread, hence
need a mechanism to guarantee the concurrence.

Best regards,
baolu