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Re: [Xen-devel] dom0 / hypervisor hang on dom0 boot

>>> On 14.05.13 at 14:35, Dietmar Hahn <dietmar.hahn@xxxxxxxxxxxxxx> wrote:
> [    6.752089] [drm:intel_sdvo_read_byte], i2c transfer returned -6
> [    6.769739] [drm:intel_sdvo_init], No SDVO device found on SDVOC
> The strange thing is, it seems that the hypervisor hangs!
> While the boot is running I can press 'h' and see the help messages between
> the linux kernel messages. When the system hangs pressing 'h' leads to 
> nothing.
> So I tried the watchdog flag on the hypervisor boot line. I can see a 
> message
> (XEN) Brought up 2 CPUs
> (XEN) Testing NMI watchdog --- CPU#0 okay. CPU#1 okay. 
> (XEN) HPET: 8 timers (2 will be used for broadcast)
> But when the system hangs nothing happens - should I get a hypervisor dump?

You should, yes, if the hypervisor is indeed hung.

Apart from trying to turn off the IOMMU as Andrew suggested,
the more interesting thing might be to turn on IOMMU debugging
("iommu=debug") to see whether there aren't any IOMMU faults.
Those shouldn't hang Xen, but then again you never know.

You may also want to know that the I relatively recently realized
that the AGP and DRM code for IGD doesn't properly handle the
Xen case: There are several instances of CONFIG_INTEL_IOMMU
dependencies which on our Xen kernel won't have the intended
effect (and on pv-ops the way this is being done can't really be
correct either afaict, as intel_iommu_gfx_mapped can't possibly
get set), since the Dom0 kernel doesn't see any IOMMU.

The necessary changes, while in our master branch, didn't get
synced over to the 12.3 branch yet.


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