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Re: [Xen-devel] Xen 4.3 development update

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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