Re: 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@suse.com>]

On 06/16/2015 10:55 AM, Ting-Wei Lan wrote:
> Juergen Gross 於 西元2015年06月16日 12:30 寫道:
>> On 06/15/2015 09:03 PM, Ting-Wei Lan wrote:
>>> 於 一，2015-06-15 於 14:55 -0400，Konrad Rzeszutek Wilk 提到：
>>>> 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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