[PATCH v2 1/2] vfio: Allow No-IOMMU mode without checking iommu_present()

On Thu, Jul 20, 2017 at 10:02:33AM +0530, Anup Patel wrote:

Not allowing No-IOMMU mode for devices already having
iommu_ops on their bus is very conservative.

We now have IOMMU (such as ARM SMMU) which can bypass
transcations when IOMMU is not configured for a given
device. In addition, it is not necessary to have all
devices on bus to be upstream to an IOMMU on that bus.

How does the SMMU know to bypass in these cases? As I explained before, the
driver-specific command line option is the wrong way to go about arranging
this.

Will