Re: [RFC PATCH 00/30] Xen Q35 Bringup patches + support for PCIe Extended Capabilities for passed through devices

[Alexey G <x1917x@gmail.com>]

A gentle RFC-ping.

Any thoughts on this? Regarding the feature as a whole. So far there
were responses mostly targeting individual patches, while I'd like to
hear about chosen approaches in general, whether the overall direction
is correct (or not), etc. It's just RFC after all, not v11. :)

I can split it into two series if that would be preferable, one for
general Q35 bring up and basic access to PCIe extended config
space via ECAM (this is what the feature was used for initially) and
the second part is providing support for PCIe Extended Capabilities
emulation infrastructure (hw/xen/xen-pt*.c in QEMU).

On Tue, 13 Mar 2018 04:33:45 +1000
Alexey Gerasimenko <x1917x@gmail.com> wrote:

>This patch series introduces support of Q35 emulation for Xen HVM
>guests (via QEMU). This feature is present in other virtualization
>products and Xen can greatly benefit from this feature as well.
>
>The main goal for implementing Q35 emulation for Xen was extending
>PCI/GPU passthrough capabilities. It's the main advantage of Q35
>emulation
>- availability of extra features for PCIe device passthrough. The most
>important PCIe-specific passthrough feature Q35 provides is a support
>for PCIe config space ECAM (aka MMCONFIG) to allow accesses to
>extended PCIe config space (>256), which is MMIO-based.  Lots of PCIe
>devices and their drivers make use of PCIe Extended Capabilities,
>whose can be accessed only using ECAM and offsets above 0x100 in PCI
>config space. Supporting ECAM is a mandatory feature for PCIe
>passthrough. Not only this allows passthrough PCIe devices to function
>properly, but opens a road to extend Xen PCIe passthrough features
>further -- eg. providing support for AER. One of possible directions
>is providing support for PCIe Resizable BARs -- a feature which likely

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