Re: Xen 4.3 development update RC2 imminent

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 22/05/13 13:49, Fabio Fantoni wrote:
> Il 21/05/2013 18:16, George Dunlap ha scritto:
>> On 05/21/2013 05:13 PM, George Dunlap wrote:
>>> On 05/21/2013 03:55 PM, Jan Beulich wrote:
>>>>>>> On 21.05.13 at 16:31, Andrew Cooper <andrew.cooper3@citrix.com> 
>>>>>>> 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...
>>> Hmm, but the code seems to indicate that the DM can handle wider
>>> entities, by "reading all ones":
>>>
>>>          if ( dir == IOREQ_READ )
>>>              memset(p_data, ~0, size);
>>>
>>> Anthony, do you want to try making that size check one size bigger
>>> (e.g., allow it to be 16 or 32)?
>> No, that obviously won't work, because of the line just following:
>>
>>     if ( (p_data != NULL) && (dir == IOREQ_WRITE) )
>>     {
>>         memcpy(&value, p_data, size);
>>         p_data = NULL;
>>     }
>>
>>
>> value is of size "long", so this won't work.
>>
>>  -George
> Thanks for help to solve this problem.
> Are there news about?
>
> Probably this is a stupid question: is this patch related to that problem?
> http://lists.xen.org/archives/html/xen-devel/2013-05/msg02142.html
>

No - that patch is unrelated to this problem.

~Andrew