From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jeremy Fitzhardinge <jeremy@goop.org>
Subject: Re: Fbdev graphics broken in xen/next dom0
Date: Fri, 12 Mar 2010 16:51:30 -0800
Message-ID: <4B9AE192.30104@goop.org>
References: <4B9AA301.6090303@tycho.nsa.gov> <4B9AB559.1070709@goop.org>
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To: Eamon Walsh <ewalsh@tycho.nsa.gov>
Cc: George Coker <gscoker@tycho.nsa.gov>, Xen-devel <xen-devel@lists.xensource.com>, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
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On 03/12/2010 04:44 PM, Eamon Walsh wrote:
> I have narrowed the problem down: it has something to do with mmap of
> /dev/fb0 not syncing.  The attached C code mmaps /dev/fb0 and writes
> some random bits.  On a configuration that does work (2.6.31.4 on
> 4.0-rc6, or xen/next on bare metal) the random bits are visible on the
> screen.  With xen/next on 4.0-rc6, nothing is visible.  Calling msync()
> before the sleep has no effect.  Also, using write() on /dev/fb0 always
> works so it appears to be mmap related.
>    

Yes.  I suspect there's a missing VM_IO in there, and so the mmap is 
mapping the wrong pages (if you're lucky you might be able to crash the 
machine to see something juicy).

     J