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[Xen-devel] 2.6.38 (FC15) with PCI passthrough fails mysteriously with i

To: Laszlo Ersek <lersek@xxxxxxxxxx>
Subject: [Xen-devel] 2.6.38 (FC15) with PCI passthrough fails mysteriously with iommu=soft..
From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Date: Wed, 1 Jun 2011 14:13:17 -0400
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
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On Wed, Jun 01, 2011 at 07:32:54PM +0200, Laszlo Ersek wrote:
> On 06/01/11 16:31, Konrad Rzeszutek Wilk wrote:
> >On Wed, Jun 01, 2011 at 01:02:02PM +0200, Laszlo Ersek wrote:
> >>(Perhaps it's best to write a separate mail about this.)
> >
> >Yes. You did use 'iommu=soft' on your bootup line right?
> I thought I did; turns out I was wrong. Sorry for the noise.
> Now I tried with "iommu=soft swiotlb=force", but this way the guest

You don't need the swiotlb=force. I wonder what page talks about that?
The Wiki mentions it is only required for older kernels - not the new ones.

> immediately disappears; it doesn't even start to produce console

It probably was panicing b/c it couldn't swizzle out 64MB
of DMA32 memory. You can find that out if you do 'earlyprintk=xenboot' and
that should print out the bootlog in your Xen debug console (if you have
configured guest_loglvl=all).

You can also do 'swiotlb=1024' to lower the amount. .. which should have worked,
except that I found it does not work - so try this patch:


Also, you can set this parameter in you guest file to analyze its stack:


using xenctx.

> output.
> # xm create -c f15-64bit-pv
> Using config file "/etc/xen/f15-64bit-pv".
> Using <class 'grub.GrubConf.GrubConfigFile'> to parse /grub/menu.lst
> Started domain f15-64bit-pv
> #
> http://wiki.xen.org/xenwiki/XenPCIpassthrough says though:
>     Bugs:
>     # Starting the DomU using pvgrub with 'iommu=soft swiotlb=force'
>     breaks pvgrub.
> Perhaps that could be the reason. Removing "swiotlb=force" and
> keeping only "iommu=soft" crashes (?) the same way.

That was .. a bug that Daniel Kiper fixed at some point. It was all in the
MiniOS. Are you using pygrub or pvgrub?

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