Re: q35 support in Xen

From: Yi Sun <yi.y.sun@linux.intel.com>
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: Sun, 17 Sep 2017 10:49:12 +0800	[thread overview]
Message-ID: <20170917024911.GA11006@yi.y.sun> (raw)
In-Reply-To: <20170915231258.00002113@gmail.com>

On 17-09-15 23:12:58, Alexey G wrote:
> Hi,
> 
> On Thu, 14 Sep 2017 16:39:32 +0800
> Yi Sun <yi.y.sun@linux.intel.com> wrote:
> 
> > Hi, Alexey,
> > 
> > Have you submitted the patches? If yes, could you please share the link?
> 
> Sorry, had a lot of work recently -- so far I've managed to submit only the
> bugfix for mentioned xen-mapcache issue with emulated AHCI DMA I/O, which
> was a main prerequisite for Q35 on Xen.
> 
> Right now I need to rebase Q35 support patches on recent changes -- there
> were multiple commits to related parts of code in both Xen and QEMU while
> Q35 patches were initially made for Xen 4.8.0 (which I'm still using at the
> moment). I'll try rebasing Q35 patches on this weekend, hopefully there
> will be no big differences with 4.8.
> 
Thanks a lot for the update! Do you have a plan for the whole feature? When
do you expect all changes can be submitted or get merged?

> 
> > > > 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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