Re: q35 support in Xen

[Alexey G <x1917x@gmail.com>]

Hi,

> I saw Anthony's patch, but your extension patch seems still in
> development. Do you have plan to upstream it? I'm also interested in
> this basically I want full PCI-e passthru capability (Current Xen does
> support passthru a PCI-e device but guest can't see configuration offset
> 256-4095 for example). I'm glad to collaborate on this.

Yes, I have plans to send patches for Q35 to the list. I've never
contributed to Xen/QEMU so far but I guess it's worth to try. It might be
a good idea to send them in batches -- split to separate parts for
libacpi, hvmloader and QEMU. There is also a number of minor
prerequisites which are required for Q35 support, ex. separating Xen
Platform device support from a selected machine (as it implemented
currently). It should be an independent option, not to be bound to a
pc/xenfv/etc machine. 

Right now many features require the emulation of something newer than a
i440 system, ex. MMCONFIG support will benefit from Q35 (or some other
PCIe-specific feature).

There still a lot of work towards a complete Q35 support in Xen of course,
but until we have a working minimum to move from there probably will be no
progress. So upstreaming a possibility to turn on the Q35 emulation and
actually run a guest on a Q35 system with some PCIe device passed through
might be a good start (if there will be no objections from maintainers).

Fixing (well, testing actually) the xen-mapcache DMA bug or validating
Stefano's patch for it is the first goal. The bug naturally affects Q35 but
in theory might be reproduced using a pc/xenfv machine (much harder though),
so it's a good candidate to start with.



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