Re: [RFC v3 1/8] vfio: Add VFIO_IOMMU_PASID_REQUEST(alloc/free)

Jacob Pan
2020-02-06T18:07:39Z

Hi Alex,

On Fri, 31 Jan 2020 12:41:06 +0000
"Liu, Yi L" <yi.l.liu@intel.com> wrote:

> > > +static int vfio_iommu_type1_pasid_free(struct vfio_iommu *iommu,
> > > + unsigned int pasid)
> > > +{
> > > + struct vfio_mm *vmm = iommu->vmm;
> > > + int ret = 0;
> > > +
> > > + mutex_lock(&iommu->lock);
> > > + if (!IS_IOMMU_CAP_DOMAIN_IN_CONTAINER(iommu)) {
> >
> > But we could have been IOMMU backed when the pasid was allocated,
> > did we just leak something? In fact, I didn't spot anything in
> > this series that handles a container with pasids allocated losing
> > iommu backing. I'd think we want to release all pasids when that
> > happens since permission for the user to hold pasids goes along
> > with having an iommu backed device.
>
> oh, yes. If a container lose iommu backend, then needs to reclaim the
> allocated PASIDs. right? I'll add it. :-)
>
> > Also, do we want _free() paths that can fail?
>
> I remember we discussed if a _free() path can fail, I think we agreed
> to let _free() path always success. :-)

Just to add some details. We introduced IOASID notifier such that when
VFIO frees a PASID, consumers such as IOMMU, can do the cleanup
therefore ensure free always succeeds.
https://www.spinics.net/lists/kernel/msg3349928.html
https://www.spinics.net/lists/kernel/msg3349930.html
This was not in my v9 set as I was considering some race conditions
w.r.t. registering notifier, gets notifications, and free call. I will
post it in v10.

Thanks,

Jacob