Re: [PATCH 05/12] iommufd/hw_pagetable: Do not populate user-managed hw_pagetables

Nicolin Chen
2023-03-10T23:32:13Z

On Fri, Mar 10, 2023 at 11:29:14AM -0400, Jason Gunthorpe wrote:
> On Thu, Mar 09, 2023 at 12:09:03AM -0800, Yi Liu wrote:
> > From: Nicolin Chen <nicolinc@nvidia.com>
> >
> > A user-managed hw_pagetable does not need to get populated, since it is
> > managed by a guest OS. Move the iopt_table_add_domain and list_add_tail
> > calls into a helper, where the hwpt pointer will be redirected to its
> > hwpt->parent if it's available.
> >
> > Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
> > Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> > ---
> > drivers/iommu/iommufd/hw_pagetable.c | 20 ++++++++++++++++++--
> > 1 file changed, 18 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/iommu/iommufd/hw_pagetable.c b/drivers/iommu/iommufd/hw_pagetable.c
> > index 16e92a1c150b..6e45ec0a66fa 100644
> > --- a/drivers/iommu/iommufd/hw_pagetable.c
> > +++ b/drivers/iommu/iommufd/hw_pagetable.c
> > @@ -43,6 +43,23 @@ int iommufd_hw_pagetable_enforce_cc(struct iommufd_hw_pagetable *hwpt)
> > return 0;
> > }
> >
> > +static int iommufd_hw_pagetable_link_ioas(struct iommufd_hw_pagetable *hwpt)
> > +{
> > + int rc;
> > +
> > + if (hwpt->parent)
>
> This should be:
>
> hwpt->domain->type != IOMMU_DOMAIN_UNMANAGED
>
> Ie if we asked the driver to alloc a domain and it allocated an
> UNMANAGED domain then it means IOMMUFD manages the mappings and it
> should be populated from the IOAS.

OK. That looks better to me.

> Arguably drivers should EOPNOTSUPP if presented with a parent in this
> situation, but still this code should be clear about the purpose.
>
> > + hwpt = hwpt->parent;
>
> And we definately shouldn't touch the parent. That is already setup
> and owned by someone else. Just return and don't do anything.

Yes.

Nic