RE: [PATCH 1/4] iommu/vt-d: Implement set device pasid op for default domain

[Tian, Kevin]

> From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
> Sent: Friday, March 3, 2023 10:49 AM
> 
> On 3/3/23 10:36 AM, Tian, Kevin wrote:
> >> From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
> >> Sent: Thursday, March 2, 2023 10:07 PM
> >>> +
> >>> +	if (!sm_supported(iommu) || !info)
> >>
> >> @info has been referenced. !info check makes no sense.
> >>
> >> Add pasid_supported(iommu).
> >>
> >> Do you need to check whether the domain is compatible for this rid
> >> pasid?
> >
> > what kind of compatibility is concerned here? In concept a pasid
> > can be attached to any domain if it has been successfully attached
> > to rid. Probably we can add a check here that RID2PASID must
> > point to the domain already.
> 
> "...if it has been successfully attached to rid..."
> 
> We should not have this assumption in iommu driver's callback. The iommu
> driver has no (and should not have) knowledge about the history of any
> domain.

but this is an op for default domain which must have been attached
to RID2PASID and any compatibility check between this domain and device
should be passed.

We can have another set_pasid for unmanaged which then need similar
check as prepare_domain_attach_device() does.

> 
> >
> >>
> >>> +		return -ENODEV;
> >>> +
> >>> +	if (WARN_ON(pasid == PASID_RID2PASID))
> >>> +		return -EINVAL;
> >>
> >> Add a call to domain_attach_iommu() here to get a refcount of the
> domain
> >> ID. And call domain_detach_iommu() in
> intel_iommu_remove_dev_pasid().
> >>
> >
> > Is it necessary? iommu core doesn't allow taking ownership
> > if !xa_empty(&group->pasid_array) so if this pasid attach succeeds
> > this device cannot be attached to another domain before pasid
> > detach is done on the current domain.
> 
> It's not about the pasid, but the domain id.
> 
> This domain's id will be set to a field of the device's pasid entry. It
> must get a refcount of that domain id to avoid use after free.
> 

If the domain still has attached device (due to this pasid usage) how could
domain id be freed?