On Wed, Dec 4, 2019 at 11:50 AM Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: > Wouldn't it also be applicable in the much simpler case where the > firmware hands over control with no IOMMU configured but also with the > busmastering bit cleared. Does firmware do this? Does the kernel > currently configure the iOMMU before enabling busmastering? We already handle this case - the kernel doesn't activate busmastering until after it does IOMMU setup.