> *
>> > This is difficult to achieve without remapping kernel memory using L2
>> > page tables, so we can unmap pages on 4K page granularity. That's
>> > going to increase TLB overhead and result in lower system performance
>
> What is the problem about mapping a 1MB buffer with the DMA API?
>
> Possibly, an IOMMU can't find space for 1MB but it's not the problem of
the DMA API.
As you have pointed out, one of the issues is that allocation can fail.
While technically VCMM allocations can fail as well, these allocations
Russell-
If a driver wants to allow a device to access memory (and cache coherency
is off/not present for device addesses), the driver needs to remap that
memory as non-cacheable. Suppose there exists a chunk of
physically-contiguous memory (say, memory reserved for device use) that
happened to be
