The IOVA allocator currently ignores host reserved regions.
As a result some chosen IOVAs may collide with some of them,
resulting in VFIO MAP_DMA errors later on. This happens on ARM
where the MSI reserved window quickly is encountered:
[0x8000000, 0x8100000]. since 5.4 kernel, VFIO returns the usable
IOVA regions. So let's enumerate them in the prospect to avoid
them, later on.

Signed-off-by: Eric Auger <eric.auger@redhat.com>
Message-id: 20200929085550.30926-2-eric.auger@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>