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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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

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