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xen-devel
RE: [Xen-devel] Support for SSE/MMX instructions.
> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
> [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of
> Keir Fraser
> Sent: 20 April 2006 17:00
> To: Petersson, Mats
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-devel] Support for SSE/MMX instructions.
>
>
> On 20 Apr 2006, at 16:37, Petersson, Mats wrote:
>
> > 1. Is anyone else working on anything like this (expanding
> the valid
> > instructions that can access memory-mapped IO to include
> either SSE or
> > MMX instructions?)
>
> I don't think so. Best would be to move all HVM I/O emulation
> to the common Xen emulator (x86_emulate.c) and add the needed
> emulation there.
I've looked a little bit at doing that - and it would probably make
sense to merge x86_emulate and the hvm handle_mmio() code, but there are
some stuff done in the handle_mmio() code that isn't done in
x86_emulate. I'll look a little further to see if I can make something
out of it [it's clearly not very clever to have two pieces of code that
decodes/emulates instructions!]
> Either way I expect that we will only need to emulate a very
> few SSE instructions (I expect this case is the result of an
> optimised memset()?).
I would expect to only see very few operations:
MOVQ, MOVDQ[AU], MOVNTQ, MOVNTDQ[AU].
And, yes in conjunction with memset/memcpy and closely related/in-lined
or specialized versions [I know 3DLabs use combinations of regular and
SSE instructions to copy data in the OpenGL library for example, and
although that gets written to regular memory, not MMIO, I can certainly
imagine that someone might use the same type of mix for other types of
operations]. For MMIO operations, I would say that the majority would
probably be copying data to or from someplace to an memory mapped IO
location. I've very rarely seen code do memset on memory-mapped IO
locations (but I guess a "clear-screen" in the form of memset((void
*)0xb8000, 0, 4000); would be such a case...)
>
> > 2. Does anyone have a hint on how we best get the MMX and SSE
> > registers so that they can be accessed in hvm/platform.c?
>
> Call unlazy_fpu(current) and then read/write the appropriate fields in
> current->arch.guest_context.fpu_ctxt.
That's what I thought - but I wanted to make sure... ;-)
--
Mats
>
> -- Keir
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel
>
>
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