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

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

On 05/21/2013 03:55 PM, Jan Beulich wrote:
> > > > On 21.05.13 at 16:31, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> > On 21/05/13 15:06, Anthony PERARD wrote:
> > > But then, once this applied, qxl is still not able to start. Xorg crash
> > > (in the guest), and here is why:
> > >
> > > (XEN) emulate.c:88:d18 bad mmio size 16
> > > (XEN) io.c:201:d18 MMIO emulation failed @ 0033:7fd2de390430: f3 0f 6f
> > > 19 41 83 e8 403
> > > (XEN) emulate.c:88:d18 bad mmio size 16
> > > (XEN) io.c:201:d18 MMIO emulation failed @ 0033:7fd2de390430: f3 0f 6f
> > > 19 41 83 e8 403
> > Disassembly of section .data:
> >
> > 0000000000000000 <.data>:
> >     0:    f3 0f 6f 19              movdqu (%rcx),%xmm3
> >
> > Xen does not support emulating SSE instructions.  We have sporadically
> > seen similar errors from Windows guests.  The best guess I have managed
> > to get so far is that %rcx is a pointer to something which Xen thinks is
> > an MMIO page.
> >
> > In this case, it looks like X is copying from MMIO into an xmm register,
> > scraping the framebuffer perhaps?  In the windows failure, it was the
> > pagescrub trying to zero ram, which clearly indicated something wonky in
> > the combined idea of the memory map.
> >
> > If Spice is doing something valid and sensible, then Xen will likely
> > need extending to be able to emulate SSE instructions.
> 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)?
I'd send you a patch but it's got to be easier to just change than to 
apply the patch...
 -George

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