[PATCH v2 5/5] iommu: Allow default domain type to be set on the kernel command line

On Tue, Mar 21, 2017 at 05:46:29PM +0000, Robin Murphy wrote:

On 21/03/17 17:21, Will Deacon wrote:

quoted

On Tue, Mar 21, 2017 at 04:45:27PM +0100, Joerg Roedel wrote:

quoted

On Fri, Mar 10, 2017 at 08:49:36PM +0000, Will Deacon wrote:

quoted

@@ -1014,8 +1027,8 @@ struct iommu_group *iommu_group_get_for_dev(struct device *dev)
 	 * IOMMU driver.
 	 */
 	if (!group->default_domain) {
-		group->default_domain = __iommu_domain_alloc(dev->bus,
-							     IOMMU_DOMAIN_DMA);
+		group->default_domain =
+			__iommu_domain_alloc(dev->bus, iommu_def_domain_type);

It would be good to have a fall-back here if we are talking to an IOMMU
driver that uses default domains, but does not support identity-mapped
domains (yet). Exynos and Rockchip IOMMU drivers seem to fall into this
category. A dev_warn() also makes sense in case allocating a identity
domain fails.

Sure, something like the diff below?

Will

--->8

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 42a842e3f95f..f787626a745d 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c

@@ -1027,10 +1027,19 @@ struct iommu_group *iommu_group_get_for_dev(struct device *dev)
 	 * IOMMU driver.
 	 */
 	if (!group->default_domain) {
-		group->default_domain =
-			__iommu_domain_alloc(dev->bus, iommu_def_domain_type);
+		struct iommu_domain *dom;
+
+		dom = __iommu_domain_alloc(dev->bus, iommu_def_domain_type);
+		if (!dom) {
+			dev_warn(dev,
+				 "failed to allocate default IOMMU domain of type %u; falling back to IOMMU_DOMAIN_DMA",
+				 iommu_def_domain_type);

Conversely, that's going to be noisy if iommu_def_domain_type was
IOMMU_DOMAIN_DMA to begin with. I think it makes sense to warn if the
user asked for a specific default domain type on the command line and
that didn't work, but maybe not to bother otherwise. Plus, if they asked
for passthrough, then not allocating a default domain at all is probably
closer to the desired result than installing a DMA ops domain would be.

You're right -- I'll hack this about to check if the default type isn't
DOMAIN_DMA before warning about the allocation failure.

Cheers,

Will