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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

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):


Lets CC Juergen

Screenshot when the system run in single user mode:


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

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
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
happened when not using Xen, so I added 'intel_iommu=off' to Linux
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


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