[RFC 1/2] iommu/dma: Restrict IOVAs to physical memory layout

-----Original Message-----
From: Robin Murphy <robin.murphy@arm.com>
Date: Tue, Jun 28, 2016 at 11:18 AM
Subject: [RFC 1/2] iommu/dma: Restrict IOVAs to physical memory layout
To: iommu at lists.linux-foundation.org, linux-arm-kernel at lists.infradead.org


Certain peripherals may be bestowed with knowledge of the physical
memory map of the system in which they live, and refuse to handle
addresses that they do not think are memory, which causes issues when
remapping to arbitrary IOVAs. Sidestep the issue by restricting IOVA
domains to only allocate addresses within ranges which match the
physical memory layout.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---

Posting this as an RFC because it's something I've been having to use
on Juno for all the PCI IOMMU development - it's pretty horrible, but I
can't easily think of a nicer solution...

Maybe I'm not getting the implications of this looking at the patch 
in isolation, but how will this impact systems that have devices
limited to 32-bit addressing?

In our memory map we have physical memory regions at:
0x00_8000_0000
0x80_8000_0000

Will devices with a 32-bit DMA mask still get 32-bit IOVAs?

Thanks,
Stuart