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

[Lu Baolu]

Hi Will,

On 2020/11/23 20:04, Will Deacon wrote:
> On Sat, Nov 21, 2020 at 09:56:17PM +0800, Lu Baolu wrote:
> > So that the vendor iommu drivers are no more required to provide the
> > def_domain_type callback to always isolate the untrusted devices.
> >
> > Link: https://lore.kernel.org/linux-iommu/243ce89c33fe4b9da4c56ba35acebf81@xxxxxxxxxx/
> > Cc: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@xxxxxxxxxx>
> > Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> > ---
> >   drivers/iommu/intel/iommu.c |  7 -------
> >   drivers/iommu/iommu.c       | 21 ++++++++++++++-------
> >   2 files changed, 14 insertions(+), 14 deletions(-)
> >
> > diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> > index af3abd285214..6711f78141a4 100644
> > --- a/drivers/iommu/intel/iommu.c
> > +++ b/drivers/iommu/intel/iommu.c
> > @@ -2916,13 +2916,6 @@ static int device_def_domain_type(struct device *dev)
> >   	if (dev_is_pci(dev)) {
> >   		struct pci_dev *pdev = to_pci_dev(dev);
> >   
> > -		/*
> > -		 * Prevent any device marked as untrusted from getting
> > -		 * placed into the statically identity mapping domain.
> > -		 */
> > -		if (pdev->untrusted)
> > -			return IOMMU_DOMAIN_DMA;
> > -
> >   		if ((iommu_identity_mapping & IDENTMAP_AZALIA) && IS_AZALIA(pdev))
> >   			return IOMMU_DOMAIN_IDENTITY;
> >   
> > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> > index 88b0c9192d8c..3256784c0358 100644
> > --- a/drivers/iommu/iommu.c
> > +++ b/drivers/iommu/iommu.c
> > @@ -1457,13 +1457,23 @@ struct iommu_group *fsl_mc_device_group(struct device *dev)
> >   }
> >   EXPORT_SYMBOL_GPL(fsl_mc_device_group);
> >   
> > -static int iommu_get_def_domain_type(struct device *dev)
> > +/* Get the mandatary def_domain type for device. Otherwise, return 0. */
> > +static int iommu_get_mandatory_def_domain_type(struct device *dev)
> >   {
> >   	const struct iommu_ops *ops = dev->bus->iommu_ops;
> > -	unsigned int type = 0;
> > +
> > +	if (dev_is_pci(dev) && to_pci_dev(dev)->untrusted)
> > +		return IOMMU_DOMAIN_DMA;
> >   
> >   	if (ops->def_domain_type)
> > -		type = ops->def_domain_type(dev);
> > +		return ops->def_domain_type(dev);
> > +
> > +	return 0;
> > +}
> > +
> > +static int iommu_get_def_domain_type(struct device *dev)
> > +{
> > +	int type = iommu_get_mandatory_def_domain_type(dev);
> >   
> >   	return (type == 0) ? iommu_def_domain_type : type;
> >   }
> > @@ -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.

Best regards,
baolu