Re: [Xen-devel] Xen 4.3 development update RC2 imminent

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Wed, May 22, 2013 at 04:05:27PM +0100, George Dunlap wrote:
> >>>>
> >>>>The emulator in the hypervisor can handle simple SSE instructions
> >>>>like the above quite well. It's not immediately clear to me why
> >>>>hvmemul_do_io() would need to limit the size to no more than a
> >>>>long's width. Perhaps the data passing to the device model may
> >>>>need adjustment to accommodate wider entities...
> >>>
> >>>Hmm, but the code seems to indicate that the DM can handle wider
> >>>entities, by "reading all ones":
> >>>
> >>>         if ( dir == IOREQ_READ )
> >>>             memset(p_data, ~0, size);
> >>>
> >>>Anthony, do you want to try making that size check one size bigger
> >>>(e.g., allow it to be 16 or 32)?
> >>
> >>No, that obviously won't work, because of the line just following:
> >>
> >>    if ( (p_data != NULL) && (dir == IOREQ_WRITE) )
> >>    {
> >>        memcpy(&value, p_data, size);
> >>        p_data = NULL;
> >>    }
> >>
> >>
> >>value is of size "long", so this won't work.
> >>
> >> -George
> >Thanks for help to solve this problem.
> >Are there news about?
> >
> >Probably this is a stupid question: is this patch related to that
> >problem?
> >http://lists.xen.org/archives/html/xen-devel/2013-05/msg02142.html
> 
> No, I'm afraid that has nothing to do with this issue.  I've only
> looked briefly at it, but it appears that the interface between Xen
> and qemu is limited to MMIO accesses of 8 bytes; changing that
> interface is not something we can really do while we're in the
> middle of doing a release.
> 
> The only work-around that would be suitable for 4.3 would be if we
> could find an option to tell the X server not to execute SSE
> instructions.  If there is no such work-around, then I'm afraid
> we're going to have to disable the interface for 4.3.  We'll put it
> on the list of work items for 4.4.
> 

Hmm, for testing, can we use cpuid to mask out SSE,
and then try qxl ? 

-- Pasi


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