Re: [Xen-devel] Test if on newer xen all SSE2 and SSE3 instructions are effectively working

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.11.13 at 13:14, Fabio Fantoni <fabio.fantoni@xxxxxxx> wrote:
> Il 21/11/2013 16:38, Andrew Cooper ha scritto:
>> On 21/11/13 15:32, George Dunlap wrote:
>>> On 21/11/13 15:22, Andrew Cooper wrote:
>>>> On 21/11/13 15:12, George Dunlap wrote:
>>>>> On Thu, Nov 21, 2013 at 10:52 AM, Fabio Fantoni
>>>>> <fabio.fantoni@xxxxxxx> wrote:
>>>>>> I'm trying to test if on newer xen all SSE2 and SSE3 instructions are
>>>>>> effectively working.
>>>>>> I tried this simple program to test SSE2:
>>>>>> http://forum.nasm.us/index.php?topic=1605.0 
>>>>>> But probably use only instructions with short operand because SSE2
>>>>>> on this
>>>>>> program is working also on old xen 4.0 where Jan Beulich patches to
>>>>>> support
>>>>>> long operands are missing.
>>>>>> Are there any minimal program to test if SSE instructions with MMIO
>>>>>> operands
>>>>>>> 8 byte are working?
>>>>> I don't see the code there doing MMIO -- it's just doing operations on
>>>>> normal RAM, which is not emulated by Xen at all, but executed natively
>>>>> by the processor.
>>>>>
>>>>> What you need is a program that will do this to an MMIO region -- that
>>>>> will be a much trickier thing to set up, I think.
>>>>>
>>>>>    -George
>>>> The problem with SSE is only when the guest performs an SSE (or larger)
>>>> operation on a piece of memory which ends up being emulated and handed
>>>> to qemu.  The ioreq protocol doesn't have a way of signalling an operand
>>>> width greater than 64 bits.
>>> I'd like to emphasize the "and" in the first sentence.  You might be
>>> able to trigger a Xen emulation in any number of ways (disabling HAP
>>> and then doing an SSE instruction on an in-use PT might do it).  But
>>> Xen allegedly already does the actual emulation correctly -- as Andy
>>> said, it's only the path to qemu that wasn't working before.
>>>
>>>   -George
>>>
>> Oops yes - I should have emphasised that a bit more.  I believe Jan
>> submitted a hacked-fix for the qemu path which fixes the immediate issue
>> (for 128bit emulation) but is in need of a redesign for wider emulation;
>> 256bit is available with AVX, and 512bit is on its way with AVX2.
>>
>> As for testing individual instructions, there is
>> tools/tests/x86_emulator/test_x86_emulator.c which tests a token few
>> instructions against Xen's emulation code, but it is far from comprehensive.
>>
>> ~Andrew
> 
> Thanks for all replies.
> I tried x86_emulator on dom0 and SSE2 instructions seems ok:

Sure. Which means you still didn't understand that you need to
try with SSE instructions accessing MMIO where the emulation
happens in qemu.

Jan


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