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

[Will Deacon]

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