Re: [Xen-devel] Xen 4.3 development update

[Fabio Fantoni <fabio.fantoni@xxxxxxx>]

Il 13/05/2013 17:39, Anthony PERARD ha scritto:
> On 13/05/13 16:15, Ian Campbell wrote:
> > On Mon, 2013-05-13 at 16:08 +0100, George Dunlap wrote:
> > > OK -- so you're saying that qxl actually *does* work, but just in a
> > > limited fashion: as long as the guest only access the standard vga
> > > interface, then you can connect over spice; but if the guest uses the
> > > special qxl interface, then it crashes.
> Of what I can understand of the few tests I've run, and what it said in
> this thread, qxl *does not* work. The standard vga is, IMHO, for
> compatibility with a guest that does not have qxl driver or early at
> boot when a qxl driver can not be started.
>
> QXL is not require in order to use SPICE. So there is no benefit for now
> of having "vga = qxl" in the guest config file.
>
> > > We don't really use qxl, so that wasn't clear at first; we thought that
> > > you were saying it didn't work at all.
> > yes, it's all much clearer to me now, thanks Fabio.
> >
> > > If it didn't work at all, then there's no point exposing functionality
> > > that can't actually work.  But since there is new functionality (albeit
> > > limited) exposed by the "qxl" option, we should keep it in.
> > >
> > > But we do need to make sure to set people's expectations properly -- our
> > > release notes will have to advertize "partial qxl support".
> > Fabio, Is there some mechanism by which we can disable the magic qxl
> > interface and only leave qxl vga enabled, i.e. to workaround the
> > unfortunate crash?
> I believe we would have to remove "vga = qxl" somehow, like adding an
> error "QXL not supported for now", unless we are able to find the issue
> between Xen and QXL.
Anthony we did some considerations as follow based on our tests:

- According to this link: 
http://xenbits.xen.org/docs/unstable/misc/libxl_memory.txt we noticed 
that on hvm domU the videomemory is actually passed separately by guest 
ram and after the build start.
- In presence of the xen hypervisor seabios gets some parameters/tables 
from hvmloader, which is not the case in absence of xen hypervisor.
- On qemu log when qxl is enabled and qemu crashes there are error about 
memory address, which may be related to some mismatch between 
hvmloader's tables and/or actual libxl memory settings.
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