Re: [Xen-devel] Xen 4.3 development update RC2 imminent

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.05.13 at 16:31, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> On 21/05/13 15:06, Anthony PERARD wrote:
>> But then, once this applied, qxl is still not able to start. Xorg crash
>> (in the guest), and here is why:
>>
>> (XEN) emulate.c:88:d18 bad mmio size 16
>> (XEN) io.c:201:d18 MMIO emulation failed @ 0033:7fd2de390430: f3 0f 6f
>> 19 41 83 e8 403
>> (XEN) emulate.c:88:d18 bad mmio size 16
>> (XEN) io.c:201:d18 MMIO emulation failed @ 0033:7fd2de390430: f3 0f 6f
>> 19 41 83 e8 403
> 
> Disassembly of section .data:
> 
> 0000000000000000 <.data>:
>    0:    f3 0f 6f 19              movdqu (%rcx),%xmm3
> 
> Xen does not support emulating SSE instructions.  We have sporadically
> seen similar errors from Windows guests.  The best guess I have managed
> to get so far is that %rcx is a pointer to something which Xen thinks is
> an MMIO page.
> 
> In this case, it looks like X is copying from MMIO into an xmm register,
> scraping the framebuffer perhaps?  In the windows failure, it was the
> pagescrub trying to zero ram, which clearly indicated something wonky in
> the combined idea of the memory map.
> 
> If Spice is doing something valid and sensible, then Xen will likely
> need extending to be able to emulate SSE instructions.

The emulator in the hypervisor can handle simple SSE instructions
like the above quite well. It's not immediately clear to me why
hvmemul_do_io() would need to limit the size to no more than a
long's width. Perhaps the data passing to the device model may
need adjustment to accommodate wider entities...

Jan


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