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

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

Hi Alexey, thanks for the ping. I think this is a good feature to have
and I would like to check it in when it is ready. I spoke with Anthony
and agreed that he will be reviewing it. Please be patient but we'll get
there :-)

On Sat, 17 Mar 2018, Alexey G wrote:
> 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@xxxxxxxxx> 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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