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RE: [Xen-devel] USB disk corruption on Xen 4.1.0 & Linux

To: Anthony Wright <anthony@xxxxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] USB disk corruption on Xen 4.1.0 & Linux
From: Ian Pratt <Ian.Pratt@xxxxxxxxxxxxx>
Date: Wed, 1 Jun 2011 09:53:44 +0100
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Thread-topic: [Xen-devel] USB disk corruption on Xen 4.1.0 & Linux
> If I use the same setup, but this time introduce the Xen 4.1.0 hypervisor I 
> get
> random blocks of sectors on the USB disk returning all zeros. Normally these
> blocks change each time I reboot, but are fixed once they've been
> established. On one occasion the blocks changed continuously each time I
> looked at the disk (I have a big file on the USB disk and I run md5sum before
> accessing it).

Does the issue go away if you limit the total amount of memory visible to xen 
to 4GB? (mem=4096M on the xen command line)

If so, I suspect this is a swiotlb or latent UHCI driver issue. The easiest way 
of working around it is just to ensure all dom0 memory gets allocated below 
4GB, but it would be good to investigate properly.


> Just to remove other possibilities I've checked the system's RAM and it's fine
> (I've seen similar problems before with dodgy RAM). If I try to access a hard
> disk or CDROM, everything is fine.
> This could be a problem with the way I've built the kernel or Xen, but it
> seems to suggest that there's a bug in Xen.
> I'm happy to try to isolate the problem further if it can't be reproduced
> elsewhere. My first suggestion would be to use a known good binary copy of
> xen 4.1.0 and/or linux if anybody can supply one.
> thanks,
> Anthony Wright
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