VT-d: add command line option for extra rmrrs

VT-d: add command line option for extra rmrrs

On some platforms firmware fails to specify RMRR regions in ACPI tables and
thus those regions will not be mapped in dom0 or guests and may cause IO
Page Faults and prevent dom0 from booting if "iommu=dom0-strict" option is
specified on the Xen command line.

New Xen command line option rmrr allows to specify such devices and
memory regions. These regions are added to the list of RMRR defined in ACPI
if the device is present in system. As a result, additional RMRRs will be
mapped 1:1 in dom0 with correct permissions.

The above mentioned problems were discovered during the PVH work with
ThinkCentre M and Dell 5600T. No official documentation was found so far
in regards to what devices and why cause this. Experiments show that
ThinkCentre M USB devices with enabled debug port generate DMA read
transactions to the regions of memory marked reserved in host e820 map.

For Dell 5600T the device and faulting addresses are not found yet.
For detailed history of the discussion please check following threads:
    http://lists.Xen.org/archives/html/xen-devel/2015-02/msg01724.html
    http://lists.Xen.org/archives/html/xen-devel/2015-01/msg02513.html

Format for rmrr Xen command line option:
    rmrr=start<-end>=[s1]bdf1[,[s1]bdf2[,...]];start<-end>=[s2]bdf1[,[s2]bdf2[,...]]
    For example, for Lenovo ThinkCentre M, use:
        rmrr=0xd5d45=0:0:1d.0;0xd5d46=0:0:1a.0
    If grub2 used and multiple ranges are specified, ';' should be
    quoted/escaped, refer to grub2 manual for more information.

Signed-off-by: Elena Ufimtseva <elena.ufimtseva@oracle.com>
Signed-off-by: Venu Busireddy <venu.busireddy@oracle.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>