VT-d: fix RMRR handling

VT-d: fix RMRR handling

Removing mapped RMRR tracking structures in dma_pte_clear_one() is
wrong for two reasons: First, these regions may cover more than a
single page. And second, multiple devices (and hence multiple devices
assigned to any particular guest) may share a single RMRR (whether
assigning such devices to distinct guests is a safe thing to do is
another question).

Therefore move the removal of the tracking structures into the
counterpart function to the one doing the insertion -
intel_iommu_remove_device(), and add a reference count to the tracking
structure.

Further, for the handling of the mappings of the respective memory
regions to be correct, RMRRs must not overlap. Add a respective check
to acpi_parse_one_rmrr().

And finally, with all of this being VT-d specific, move the cleanup
of the list as well as the structure type definition where it belongs -
in VT-d specific rather than IOMMU generic code.

Note that this doesn't address yet another issue associated with RMRR
handling: The purpose of the RMRRs as well as the way the respective
IOMMU page table mappings get inserted both suggest that these regions
would need to be marked E820_RESERVED in all (HVM?) guests' memory
maps, yet nothing like this is being done in hvmloader. (For PV guests
this would also seem to be necessary, but may conflict with PV guests
possibly assuming there to be just a single E820 entry representing all
of its RAM.)

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Xiantao Zhang <xiantao.zhang@intel.com>