q35 support in Xen

[olivierlambert]

Patch Xen to emulate the Q35 chipset to enable PCIe/GPU passthrough.

Xen currently only emulates the i440 chipset. i440 does not support PCI extended configuration registers (image attached). This patch series would support emulating the Q35 chipset, allowing guests to use devices that require PCIe extended configuration registers.

One reason the original patchset was rejected because they assumed that there would only be one IOREQ server per VM, which is not a generalizable assumption because Xen does support more than one per VM. The discussion thread starts here: https://lore.kernel.org/xen-devel/62c7a3037bb9f5631542f635dc36ae3338c7bf47.1520867741.git.x1917x@gmail.com/

• Q35 datasheet is here: https://www.intel.com/Assets/PDF/datasheet/316966.pdf
• The ICH9 spec is also useful: https://www.intel.com/content/www/us/en/io/io-controller-hub-9-datasheet.html

[tklengyel]

Just for reference, the patchset on xen-devel is https://lists.xenproject.org/archives/html/xen-devel/2018-03/msg01176.html
There was another patchset that implemented q35 support at OpenXT/xenclient-oe#729

[beshleman]

Awesome, thanks for the reference to the patchset Tamas