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

[Baolu Lu]

On 5/20/24 11:26 AM, Tian, Kevin wrote:
> > From: Baolu Lu <baolu.lu@xxxxxxxxxxxxxxx>
> > Sent: Monday, May 20, 2024 8:41 AM
> >
> > 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)
>
> "currently only designed for IOMMUFD" doesn't sound correct.
>
> design-wise this can be used by anyone which relies on the handle.
> There is nothing tied to IOMMUFD.
>
> s/designed for/used by/ is more accurate.

Done.

Best regards,
baolu