Re: q35 support in Xen

From: Stefano Stabellini <sstabellini@kernel.org>
To: Alexey G <x1917x@gmail.com>
Cc: Jason Dickens <jdickens@grammatech.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Wei Liu <wei.liu2@citrix.com>,
	xen-devel@lists.xen.org,
	Anthony PERARD <anthony.perard@citrix.com>,
	Chao Peng <chao.p.peng@linux.intel.com>
Subject: Re: q35 support in Xen
Date: Thu, 29 Jun 2017 13:18:34 -0700 (PDT)	[thread overview]
Message-ID: <alpine.DEB.2.10.1706291317410.2919@sstabellini-ThinkPad-X260> (raw)
In-Reply-To: <20170630060351.0000640a@gmail.com>

On Fri, 30 Jun 2017, Alexey G wrote:
> 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).

Sure, it is fine by me. Patches are very welcome!

> 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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