Second kexec_file_load (but not kexec_load) fails on i915 if CONFIG_INTEL_IOMMU_DEFAULT_ON=n

[Pingfan Liu]

On Sat, Jul 5, 2025 at 4:12 AM Askar Safin <safinaskar at zohomail.com> wrote:
>
>  ---- On Fri, 04 Jul 2025 12:29:01 +0400  Jani Nikula <jani.nikula at linux.intel.com> wrote ---
>  > Thanks for the detailed debug info. I'm afraid all I can say at this
>  > point is, please file all of this in a bug report as described in
>  > [1]. Please add the drm.debug related options, and attach the dmesgs and
>  > configs in the bug instead of pointing at external sites.
>
> Okay, now let me speculate how to fix this bug. :) I think someone with moderate kexec understanding
> and with Intel GPU should do this: reproduce the bug and then slowly modify kexec_file_load code until it
> becomes kexec_load code. (Or vice versa.) In the middle of this modification the bug stops to reproduce,
> and so we will know what exactly causes it.
>
> kexec_file_load and kexec_load should behave the same. If they do not, then we should
> understand, why. We should closely review their code.
>
> Also, in case of kexec_load kernel uncompressing and parsing performed by "kexec" userspace
> tool, and in case of kexec_file_load by kernel. So we should closely review this two uncompressing/parsing code fragments.
> I think that this bug is related to kexec, not to i915. And thus it should be fixed by kexec people, not by i915 people. (But I may be wrong.)
>

I tend to agree with Baoquan on this scene when kexec rebooted with a
graphic card.
I heard that this was due to the missed initialization on the graphic
card by the firmware in the kexec reboot process. But it is not an
official explanation. If any experts could enlighten me on this, I'd
really appreciate it.

IMHO, you could try blacklisting the i915 module to see if
kexec_file_load works without issues - this would help narrow down the
culprit.

Thanks,

Pingfan

> But okay, I reported it to that bug tracker anyway: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/14598
>
> Maybe there is separate kexec bug tracker?
>
> Also, your bug tracker is cool. One can attach files in the middle of report. Why not whole kernel uses it? :)
>
> --
> Askar Safin
> https://types.pl/@safinaskar
>
>