Re: [Xen-devel] mmx sse emulation

[Andre Przywara <andre.przywara@xxxxxxx>]

Ashish Bijlani wrote:
> Hi,
>
> I want to emulate mmx/sse for hvm guests when applications inside hvm
> guests are compiled for mmx/sse but the underlying hardware doesn't
> support mmx/sse.
First: HVM guests require a virtualization capable processor. AFAIK all 
these processors support at least SSE2 (if not SSE3). So why do you want 
to emulate these instructions?
Second: Applications should check the CPUID bit before using instruction 
set extension. So, if the host processor does not support MMX/SSE, the 
guest shouldn't see this bit, too. And I doubt that you are faster with 
emulating SSE compared to legacy x87-FPU executed natively.
So, what is the use-case of your proposal? Or am I missing something here?

Regards,
Andre.

> What is the best place to do this? i'm looking at
> x86_emulate but i dunno if that is the best place to put the emulation
> layer. any suggestions?? also, currently movq emulation is present in
> x86_emulate for handling mmio. however, i realized that get_fpu fails
> if the hardware doesn't have mmx capability. is it true or am i
> missing something here?
>
> Thanks,
> Ashish
--
Andre Przywara
AMD-OSRC (Dresden)
Tel: x84917


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