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Re: [Xen-devel] DL385 G2 - PCI-DMA: Random memory would be DMAed

To: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] DL385 G2 - PCI-DMA: Random memory would be DMAed
From: Zachary Richmond <admin.ihsdoor@xxxxxxxxx>
Date: Fri, 19 Oct 2007 14:29:00 -0500
Cc: "Langsdorf, Mark" <mark.langsdorf@xxxxxxx>
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Langsdorf, Mark wrote:
To answer Mark's question:

 > What kernel are you using?

from gentoo: xen-sources-2.6.20-r6

Regarding the full error message, all I am getting is:

     kernel panic not syncing: PCI-DMA: Random memory would be DMAed

since the machine is rebooting after that. There maybe somewhere else to get more detail, but beyond dmesg or
messages I am not sure where else to look.

For some reason, your kernel is running with pci-gart.c
enabled, and dom0 is trying to allocate DMA through the
AGP GART in your AMD64 processor's Northbridge. I didn't think Xen supported pci-gart, but maybe I missed
a changeset.

At any rate, passing iommu=soft should disable the pci-gart
and allow you to use bounce buffering.  Hopefully, that
should clear up your problem.

-Mark Langsdorf
Operating System Research Center
AMD




Unfortunately I am still having the problem. Having booted off a cd to preserve log files a quick grep on dmesg shows:

        PCI-DMA: Using software bounce buffering for IO (SWIOTLB)

So it is enabled, but still the kernel panic. Any other ideas on where to poke around?

        Thanks,

        Zak





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