Re: [PATCH v5 5/9] iommufd: Add iommufd fault object

[Baolu Lu]

On 5/15/24 3:57 PM, Tian, Kevin wrote:
> > From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
> > Sent: Wednesday, May 8, 2024 6:05 PM
> >
> > On 2024/5/8 8:11, Jason Gunthorpe wrote:
> > > On Tue, Apr 30, 2024 at 10:57:06PM +0800, Lu Baolu wrote:
> > > > diff --git a/drivers/iommu/iommu-priv.h b/drivers/iommu/iommu-priv.h
> > > > index ae65e0b85d69..1a0450a83bd0 100644
> > > > --- a/drivers/iommu/iommu-priv.h
> > > > +++ b/drivers/iommu/iommu-priv.h
> > > > @@ -36,6 +36,10 @@ struct iommu_attach_handle {
> > > >    			struct device	*dev;
> > > >    			refcount_t	users;
> > > >    		};
> > > > +		/* attach data for IOMMUFD */
> > > > +		struct {
> > > > +			void		*idev;
> > > > +		};
> > > We can use a proper type here, just forward declare it.
> > >
> > > But this sequence in the other patch:
> > >
> > > +       ret = iommu_attach_group(hwpt->domain, idev->igroup->group);
> > > +       if (ret) {
> > > +               iommufd_fault_iopf_disable(idev);
> > > +               return ret;
> > > +       }
> > > +
> > > +       handle = iommu_attach_handle_get(idev->igroup->group,
> > IOMMU_NO_PASID, 0);
> > > +       handle->idev = idev;
> > >
> > > Is why I was imagining the caller would allocate, because now we have
> > > the issue that a fault capable domain was installed into the IOMMU
> > > before it's handle could be fully setup, so we have a race where a
> > > fault could come in right between those things. Then what happens?
> > > I suppose we can retry the fault and by the time it comes back the
> > > race should resolve. A bit ugly I suppose.
> >
> > You are right. It makes more sense if the attached data is allocated and
> > managed by the caller. I will go in this direction and update my series.
> > I will also consider other review comments you have given in other
> > places.
>
> Does this direction imply a new iommu_attach_group_handle() helper
> to pass in the caller-allocated handle pointer or exposing a new
> iommu_group_set_handle() to set the handle to the group pasid_array
> and then having iomm_attach_group() to update the domain info in
> the handle?

I will add new iommu_attach/replace/detach_group_handle() helpers. Like
below:

+/**
+ * iommu_attach_group_handle - Attach an IOMMU domain to an IOMMU group
+ * @domain: IOMMU domain to attach
+ * @group: IOMMU group that will be attached
+ * @handle: attach handle
+ *
+ * Returns 0 on success and error code on failure.
+ *
+ * This is a variant of iommu_attach_group(). It allows the caller to 
provide
+ * an attach handle and use it when the domain is attached. This is 
currently
+ * only designed for IOMMUFD to deliver the I/O page faults.
+ */
+int iommu_attach_group_handle(struct iommu_domain *domain,
+                             struct iommu_group *group,
+                             struct iommu_attach_handle *handle)

Best regards,
baolu