Re: [Xen-devel] Is: graphics corruption with 'xen: Support Xen pv-domains using PAT." Was:Re: [BUG] Characters on the screen are broken on Linux >= 3.19 with VT-d enabled

[Juergen Gross <jgross@xxxxxxxx>]

On 06/15/2015 09:03 PM, Ting-Wei Lan wrote:
> æ äï2015-06-15 æ 14:55 -0400ïKonrad Rzeszutek Wilk æåï
> > On Sat, Jun 13, 2015 at 12:43:14AM +0800, Ting-Wei Lan wrote:
> > > When using Linux >= 3.19 as the dom0 kernel, characters on the
> > > screen become
> > > broken after the graphic driver is loaded. The commit that breaks
> > > it is
> > > (found by git bisect):
> > >
> > >
> > > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/com
> > > mit/?id=47591df
> > Lets CC Juergen
> > > Screenshot when the system run in single user mode:
> > >
> > >    https://bugs.freedesktop.org/attachment.cgi?id=115079
Are those messages to be expected:

(XEN) Scrubbing Free RAM on 1 nodes using 2 CPUs
(XEN) [VT-D]DMAR:[DMA Write] Request device [0000:00:02.0] fault addr 
b61eef000, iommu reg = ffff82c000203000
(XEN) [VT-D]DMAR: reason 05 - PTE Write access is not set
(XEN) 
..................................................................done.
I'm not familiar with VT-D internals, but seeing these messages for the
video device during RAM scrubbing makes wonder if everything is correct
regarding the VT-D and memory setup...

> > > I still remember that there was a similar problem found two years
> > > ago on the
> > > same hardware with similar broken screen output and it also crashed
> > > after
> > > Xorg was started, but I cannot confirm that they are the same
> > > problems. I
> > > don't know whether error messages are simliar.
> > >
> > > The old problem happens on Linux 3.7 ~ 3.10 with VT-d enabled. It
> > > only
> > > happened when not using Xen, so I added 'intel_iommu=off' to Linux
> > > boot
> > > arguments to workaround it.
Hmm, do you see any chance in finding the commit which made it working
again? Perhaps there was some workaround for this hardware which is
missing in Xen now...


Juergen

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