Re: [Xen-devel] [PATCH] libxl: Remove qxl support for the 4.3 release

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.09.13 at 16:10, Fabio Fantoni <fabio.fantoni@xxxxxxx> wrote:
> Il 05/07/2013 18:59, George Dunlap ha scritto:
>> On Wed, May 29, 2013 at 11:25 PM, Andrew Cooper
>> <andrew.cooper3@xxxxxxxxxx> wrote:
>>> On 29/05/2013 08:43, Ian Campbell wrote:
>>>> On Tue, 2013-05-28 at 19:09 +0100, Keir Fraser wrote:
>>>>> On 28/05/2013 17:51, "Ian Jackson" <Ian.Jackson@xxxxxxxxxxxxx> wrote:
>>>>>
>>>>>> George Dunlap writes ("[PATCH] libxl: Remove qxl support for the 4.3
>>>>>> release"):
>>>>>>> The qxl drivers for Windows and Linux end up calling instructions
>>>>>>> that cannot be used for MMIO at the moment.  Just for the 4.3 release,
>>>>>>> remove qxl support.
>>>>>>>
>>>>>>> This patch should be reverted as soon as the 4.4 development window 
>>>>>>> opens.
>>>>>>>
>>>>>>> The issue in question:
>>>>>>>
>>>>>>> (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
>>>>>>>
>>>>>>> The instruction in question is "movdqu (%rcx),%xmm3".  Xen knows how
>>>>>>> to emulate it, but unfortunately %xmm3 is 16 bytes long, and the 
>>>>>>> interface
>>>>>>> between Xen and qemu at the moment would appear to only allow MMIO 
>>>>>>> accesses
>>>>>>> of 8 bytes.
>>>>>>>
>>>>>>> It's too late in the release cycle to find a fix or a workaround.
>>>>>> Acked-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
>>>>> It could be plumbed through hvmemul_do_io's multi-cycle read/write logic,
>>>>> and done as two 8-byte cycles to qemu. This would avoid bloating the ioreq
>>>>> structure that communicates to qemu.
>>>> Are you proposing we do this for 4.3? I'm not sure how big that change
>>>> would be in terms of impact (just that one instruction, any 16 byte
>>>> operand?).
>>>>
>>>> Of course even if we did this for 4.3 we don't know what the next issue
>>>> will be with QXL.
>>>>
>>>> Ian.
>>> Furthermore, AVX instruction emulation would require support for 32byte
>>> operands.  I don't see the multi-cycle logic scaling sensibly.
>> Andrew, Keir, Jan, does any one of you fancy taking this on for 4.4?
> 
> Is there someone that can add full support for SSE on hvm domUs?
> Thanks for any reply.

I was intending to take a look whether this can be done without
altering the interface with qemu, in which case I may be able to
get this implemented. But as long as higher priority work keeps
showing up, this will continue to get deferred...

Jan


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