VT-d: deal with 5500/5520/X58 errata

VT-d: deal with 5500/5520/X58 errata

http://www.intel.com/content/www/us/en/chipsets/5520-and-5500-chipset-ioh-specification-update.html

Stepping B-3 has two errata (#47 and #53) related to Interrupt
remapping, to which the workaround is for the BIOS to completely disable
interrupt remapping.  These errata are fixed in stepping C-2.

Unfortunately this chipset stepping is very common and many BIOSes are
not disabling interrupt remapping on this stepping .  We can detect this in
Xen and prevent Xen from using the problematic interrupt remapping feature.

The Intel 5500/5520/X58 chipset does not support VT-d
Extended Interrupt Mode(EIM). This means the iommu_supports_eim() check
always fails and so x2apic mode cannot be enabled in Xen before this quirk
disables the interrupt remapping feature.

Signed-off-by: Malcolm Crossley <malcolm.crossley@citrix.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Gate the function call to check the quirk on interrupt remapping being
requested to get enabled, and upon failure disable the IOMMU to be in
line with what the changes for XSA-36 (plus follow-ups) did.

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