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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 11:32 AM, èæç wrote:
æ äï2015-06-16 æ 11:06 +0200ïJuergen Gross æåï
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?
But Linux provides 'intel_iommu=igfx_off' to workaround the problem.
Does Xen provide similar things?
Not that I know of. The question is whether you really need VT-d, and if
yes, why. You could still switch the iommu off for dom0 by setting
iommu=dom0-passthrough in the Xen command line (your hardware might not
support it, though).
Juergen
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