Re: [PATCH v1 1/8] iommu: Add iommu_group_replace_domain()

[Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>]

On 1/7/22 1:06 AM, Jason Gunthorpe wrote:
> On Thu, Jan 06, 2022 at 10:20:46AM +0800, Lu Baolu wrote:
> > Expose an interface to replace the domain of an iommu group for frameworks
> > like vfio which claims the ownership of the whole iommu group.
> >
> > Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> >   include/linux/iommu.h | 10 ++++++++++
> >   drivers/iommu/iommu.c | 37 +++++++++++++++++++++++++++++++++++++
> >   2 files changed, 47 insertions(+)
> >
> > diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> > index 408a6d2b3034..66ebce3d1e11 100644
> > +++ b/include/linux/iommu.h
> > @@ -677,6 +677,9 @@ void iommu_device_unuse_dma_api(struct device *dev);
> >   int iommu_group_set_dma_owner(struct iommu_group *group, void *owner);
> >   void iommu_group_release_dma_owner(struct iommu_group *group);
> >   bool iommu_group_dma_owner_claimed(struct iommu_group *group);
> > +int iommu_group_replace_domain(struct iommu_group *group,
> > +			       struct iommu_domain *old,
> > +			       struct iommu_domain *new);
> >   
> >   #else /* CONFIG_IOMMU_API */
> >   
> > @@ -1090,6 +1093,13 @@ static inline bool iommu_group_dma_owner_claimed(struct iommu_group *group)
> >   {
> >   	return false;
> >   }
> > +
> > +static inline int
> > +iommu_group_replace_domain(struct iommu_group *group, struct iommu_domain *old,
> > +			   struct iommu_domain *new)
> > +{
> > +	return -ENODEV;
> > +}
> >   #endif /* CONFIG_IOMMU_API */
> >   
> >   /**
> > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> > index 72a95dea688e..ab8ab95969f5 100644
> > +++ b/drivers/iommu/iommu.c
> > @@ -3431,3 +3431,40 @@ bool iommu_group_dma_owner_claimed(struct iommu_group *group)
> >   	return user;
> >   }
> >   EXPORT_SYMBOL_GPL(iommu_group_dma_owner_claimed);
> > +
> > +/**
> > + * iommu_group_replace_domain() - Replace group's domain
> > + * @group: The group.
> > + * @old: The previous attached domain. NULL for none.
> > + * @new: The new domain about to be attached.
> > + *
> > + * This is to support backward compatibility for vfio which manages the dma
> > + * ownership in iommu_group level.
>
> This should mention it can only be used with iommu_group_set_dma_owner()

Sure.

> > +	if (old)
> > +		__iommu_detach_group(old, group);
> > +
> > +	if (new) {
> > +		ret = __iommu_attach_group(new, group);
> > +		if (ret && old)
> > +			__iommu_attach_group(old, group);
> > +	}
>
> The sketchy error unwind here gives me some pause for sure. Maybe we
> should define that on error this leaves the domain as NULL
>
> Complicates vfio a tiny bit to cope with this failure but seems
> cleaner than leaving it indeterminate.

Fair enough.

> Jason

Best regards,
baolu