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Re: [Xen-devel] I cannot get any message from domU by console / pv_ops d

To: Pasi Kärkkäinen <pasik@xxxxxx>
Subject: Re: [Xen-devel] I cannot get any message from domU by console / pv_ops domU kernel crashes with xen_create_contiguous_region failed
From: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
Date: Tue, 22 Dec 2009 09:20:15 +0000
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, ?????? <peb1611@xxxxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
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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


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