[Xen-devel] [PATCH 0 of 1] Intel VT-d fix.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On a SuperMicro X8DTN+ I found Linux baremetal booting fine, while
Xen would hang while enabling PCI-X devices, such as:

(XEN) CPU 10 initiali[    5.118255] scsi0 : 3ware Storage Controller
[    5.118898] 3w-xxxx: scsi0: Found a 3ware Storage Controller at 0xc100, IRQ: 
52.
(XEN) do_IRQ: 1.40 No irq handler for vector (irq -1)
[   25.711139] scsi 0:0:0:0: WARNING: Command (0x12) timed out, resetting card.
[   47.191274] scsi 0:0:0:0: WARNING: Command (0x0) timed out, resetting card.
[   58.671124] scsi 0:0:0:0: Device offlined - not ready after error recovery
[   79.711194] scsi 0:0:1:0: WARNING: Command (0x12) timed out, resetting card.
[  101.191071] scsi 0:0:1:0: WARNING: Command (0x0) timed out, resetting card.
[  112.671065] scsi 0:0:1:0: Device offlined - not ready after error recovery
[  133.710995] scsi 0:0:2:0: WARNING: Command (0x12) timed out, resetting card.
[  155.190891] scsi 0:0:2:0: WARNING: Command (0x0) timed out, resetting card.


Traced it down the fact that I've three IOAPICs, but only one DRHD. The
DRHD covers the first IOAPIC, but not the other two. Well, the PCI-X device
was on the last IOAPIC, which was not under the DRHD control.

Linux upstream has a check where it looks for all the IOAPICs covered by the 
DRHDs
and compares them with the IOAPICs it found via MADT. If the count is off it
disables x2APIC.

This patch follows that logic.



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