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

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

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


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