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

[Nicolin Chen]

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@xxxxxxxxxx>
> > 
> > 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@xxxxxxxxxx>
> > Signed-off-by: Yi Liu <yi.l.liu@xxxxxxxxx>
> > ---
> >  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