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

Tian, Kevin
2024-05-15T07:57:39Z

> From: Baolu Lu <baolu.lu@linux.intel.com>
> 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?