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

To: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
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: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Date: Tue, 22 Dec 2009 09:35:40 -0500
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, ?????? <peb1611@xxxxxxxxx>
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On Tue, Dec 22, 2009 at 09:20:15AM +0000, Ian Campbell wrote:
> 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.

Not so. You can still make the call even if you don't have PCI passthrough
enabled. The up call is just to replace MFNs.

> 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

I concur. It should also give the error code. I am working on re-writting that
code since the upstream now has some form of registration/de-registration that
we could take advantage off.

> if it hasn't got privilege to make the fixups it isn't going to have any
> devices.
> Ian.
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