Re: [Xen-devel] I cannot get any message from domU by console / pv_ops domU kernel crashes with xen_create_contiguous_region failed

[Michael D Labriola <mlabriol@xxxxxxxx>]

xen-devel-bounces@xxxxxxxxxxxxxxxxxxx wrote on 12/22/2009 04:20:15 AM:

> On Tue, 2009-12-22 at 08:42 +0000, Pasi Kärkkäinen wrote:
> > >    (early) [    0.000000] PCI-DMA: Using Xen software bounce
> > buffering for IO
> > >    (Xen-SWIOTLB)
> > >    (early) [    0.000000] Kernel panic - not syncing:
> > >    <3>xen_create_contiguous_region failed
> > > 
> > 
> > Did you try cgroup_disable=memory kernel option? 
> 
> I think this is more likely to relate to the failure to initialise
> swiotlb due to the failure of xen_create_contiguous_region, leading to a
> panic. IIRC the guest won't be privileged enough to make this call
> unless it has PCI passthrough enabled.
> 
> In a pre-pvops kernel the swiotlb would be inactive in a domU unless
> specifically requested on the command line but in Jeremy's xen/master
> branch it looks like it is unconditionally enabled for dom0 and domU as
> a consequence of:
>         commit 4bc6b1a9dd5d7447af8c3d27c1449f73f5f764ec
>         Author: root <root@xxxxxxxxxxxxxxxxxxxxx>
>         Date:   Thu Nov 5 16:33:10 2009 -0500
> 
>             Enable Xen-SWIOTLB if running in [non-]privileged and 
> disable the Xen-IOMMU if an IOMMU is detected.
> 
> On a related note I don't think the xen-swiotlb code should panic() if
> it cannot allocate the contiguous region (at least in domU). Chances are
> if it hasn't got privilege to make the fixups it isn't going to have any
> devices.

I ran into the same problem yesterday, traced it back to that exact 
commit.  Reverting it makes my domUs work, but feels like the wrong thing 
to do.  How do I make sure xen_create_contiguous_region is privileged 
enough?  I've got the PCI frontend and backend  built in to my kernel 
(used the x86 fedora .config from the pv_ops wiki).

-Mike


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