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 06/16/2015 10:55 AM, Ting-Wei Lan wrote:
> Juergen Gross æ èå2015å06æ16æ 12:30 åé:
> > 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...
> After some tests, I found the information I provided before was
> incorrect. It seems the problem happens on all Linux >= 3.7, including
> Linux 4.0.5, so the old problem was never fixed. Here are some 'dmesg |
> grep -i iommu' outputs.
So a Xen-specific error is rather improbable, correct?

I'd continue with sending the new information to the Intel graphics
team.


Juergen

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