[Bug 298061] page fault in i915_gem_context_open

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=298061

Paul Floyd <pjfloyd@wanadoo.fr> changed:

           What    |Removed                     |Added
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                 CC|                            |pjfloyd@wanadoo.fr

--- Comment #3 from Paul Floyd <pjfloyd@wanadoo.fr> ---
I can reproduce a kernel page fault with drm-612-kmod on FreeBSD 15.1, using
the Intel UHD Graphics P630 (Comet Lake, PCI device ID 8086:9bf6) in a Dell
Precision 7550.

System details

    FreeBSD kernel: 15.1-RELEASE-p5

    Userland: 15.1-RELEASE-p6

    Original DRM package: drm-612-kmod-6.12.85.1501000_2

    DRM package repository: kmods_quarterly_1

    GPU: Intel UHD Graphics P630, Comet Lake (device ID 9bf6)

    The laptop also has an NVIDIA Quadro T1000 Mobile.

With kld_list="i915kms" in /etc/rc.conf, the system panicked during boot. I
commented that out, rebooted and tried "sudo kldload i915kms" and that also
paniced. The crash dump contains two relevant page-fault backtraces:

    During kldload, in i915_gem_context_open+0x1a7, followed by i915_gem_open,
drm_file_alloc, and i915_driver_probe.

    In the linuxkpi_long_wq_5 worker thread, in
drm_dp_mst_port_add_connector+0x125, called from drm_dp_send_link_address,
drm_dp_check_and_send_link_address, and drm_dp_mst_link_probe_work.

The second backtrace occurs during DisplayPort MST probing. The boot log also
reports an LSPCON probe failure on port D.

Workaround tested

I switched from drm-612-kmod to the available quarterly package:

drm-61-kmod-6.1.128.1501000_11

With the 6.1 package installed, sudo kldload i915kms succeeded, and service
sddm onestart also succeeded.

This provides evidence that the failure is associated with the 6.12 DRM stack
on this system. I have not yet established whether the 6.1 driver resolves all
boot, display, and suspend/resume issues, or whether a particular upstream
change fixes the 6.12 failure.

The crash dump and relevant system information are available for further
investigation.

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