The case is 1) disabling iommu for IGD, unilaterally since i915 + gm45
doesn't play well together. Iommu is still desired to isolate usb and
network devices, so we don't want to disable iommu completely. The side
effect of this would be to have IGD only for dom0, which would also
completely make sense in this use case.

The point is the iommu=no-igfx doesn't fix the issue, since remapping seems
to still happen for IGD. Does that make sense ?

Le lun. 25 janv. 2016 09:30, Jan Beulich <JBeulich@suse.com> a écrit :

> >>> On 23.01.16 at 08:38, <thierry.laurion@gmail.com> wrote:
> > Thinkpad x200 p8600 laptops have vt-d, vt-x and tpm. They also have intel
> > integrated graphics 4 Series (gm45 chipset), supported through i915
> driver.
> >
> > In December, a fix got introduced to Xen 4.6 through iommu=no-igfx
> switch.
> > Before that fix, it was impossible to boot xen without passing iommu=0.
> >
> > With iommu=no-igfx passed on, Qubes boots xen, kernel, dom0 and domu
> until
> > some graphic rendering is done from a domu to dom0 xserver.
> >
> > I'm trying to push forward IOMMU support of gm45 chipset here. The
> problem
> > is between i915 and xen iommu support for sure, but there is no crash or
> > interesting debugging information given on a serial console.
>
> To be honest, even after having read you second mail I'm not quite
> clear what it you want and/or what doesn't work. Adding some
> guessing, I could interpret the above as you wanting to pass through
> the graphics device. If that's the case, then this is quite clearly a
> pretty bad idea with the IOMMU behind it disabled.
>
> Jan
>
>