Re: [PATCH v9 1/4] iommu: Move def_domain type check for untrusted device into core

From: Will Deacon
Date: Mon Nov 23 2020 - 08:07:49 EST


Hi Baolu,

On Mon, Nov 23, 2020 at 08:55:17PM +0800, Lu Baolu wrote:
> On 2020/11/23 20:04, Will Deacon wrote:
> > On Sat, Nov 21, 2020 at 09:56:17PM +0800, Lu Baolu wrote:
> > > @@ -1645,13 +1655,10 @@ struct __group_domain_type {
> > > static int probe_get_default_domain_type(struct device *dev, void *data)
> > > {
> > > - const struct iommu_ops *ops = dev->bus->iommu_ops;
> > > struct __group_domain_type *gtype = data;
> > > unsigned int type = 0;
> > > - if (ops->def_domain_type)
> > > - type = ops->def_domain_type(dev);
> > > -
> > > + type = iommu_get_mandatory_def_domain_type(dev);
> >
> > afaict, this code is only called from probe_alloc_default_domain(), which
> > has:
> >
> > /* Ask for default domain requirements of all devices in the group */
> > __iommu_group_for_each_dev(group, &gtype,
> > probe_get_default_domain_type);
> >
> > if (!gtype.type)
> > gtype.type = iommu_def_domain_type;
> >
> > so is there actually a need to introduce the new
> > iommu_get_mandatory_def_domain_type() function, given that a type of 0
> > always ends up resolving to the default domain type?
>
> Another consumer of this helper is in the next patch:
>
> + dev_def_dom = iommu_get_mandatory_def_domain_type(dev);
> +
> + /* Check if user requested domain is supported by the device or not */
> + if (!type) {
> + /*
> + * If the user hasn't requested any specific type of domain and
> + * if the device supports both the domains, then default to the
> + * domain the device was booted with
> + */
> + type = iommu_get_def_domain_type(dev);
> + } else if (dev_def_dom && type != dev_def_dom) {
> + dev_err_ratelimited(prev_dev, "Device cannot be in %s domain\n",
> + iommu_domain_type_str(type));
> + ret = -EINVAL;
> + goto out;
> + }
>
> I also added the untrusted device check in
> iommu_get_mandatory_def_domain_type(), so that we don't need to care
> about this in multiple places.

I see, but isn't this also setting the default domain type in the case that
it gets back a type of 0? I think it would be nice to avoid having both
iommu_get_mandatory_def_domain_type() and iommu_get_def_domain_type() of we
can, as it's really not clear which one to use when and what is meant by
"mandatory" imo.

Will