Bug#1012210: linux-image-5.10.0-14-amd64: Kernels of Bullseye and Testing (5.10 and 5.17) hang at boot

[Markus Kolb <debian@tower-net.de>]

Because the kernel.org 5.10.113 with my stripped down config is running 
successful,
I've rebuilt this kernel.org 5.10.113 with the Debian config 
/boot/config-5.10.0-14-amd64 via make oldconfig.
There are some differences between kernel.org and Debian in the config, 
I've put the config diff bug-1012210-kernel-config-changes.patch in the 
attached tar.xz.
This kernel also boots successful.

I think the problem is introduced by a Debian patch which handles the 
config
  CONFIG_INTEL_IOMMU_DEFAULT_ON_INTGPU_OFF=y
because this is not available in kernel.org 5.10.113.

And the Debian kernel
  linux-image-5.10.0-14-amd64           5.10.113-1
boots successful when I set the boot option
  intel_iommu=on,igfx_off
which is only needed with the Debian kernel and not any version from 
kernel.org.

In the boot log of Debian kernel are the additional lines
[    0.050433] DMAR: IOMMU enabled
[    0.050434] DMAR: Disable GFX device mapping
...
[    1.373598] DMAR: No ATSR found
[    1.373721] DMAR: dmar2: Using Register based invalidation
[    1.373767] DMAR: dmar0: Using Register based invalidation
[    1.373810] DMAR: dmar3: Using Register based invalidation
...
[    1.391563] DMAR: Intel(R) Virtualization Technology for Directed I/O

The kernel boot logs
  dmesg-5.10.113.txt (kernel.org without any boot options)
  dmesg-5.10.0-14-amd64.txt (Debian with boot option 
intel_iommu=on,igfx_off)
are also in the attached tar.xz.

In the patches

  
https://salsa.debian.org/kernel-team/linux/-/blob/bullseye-security/debian/patches/features/x86/intel-iommu-add-kconfig-option-to-exclude-igpu-by-default.patch
  
https://salsa.debian.org/kernel-team/linux/-/blob/bullseye-security/debian/patches/features/x86/intel-iommu-add-option-to-exclude-integrated-gpu-only.patch

there is introduced the kernel config option
  INTEL_IOMMU_DEFAULT_ON_INTGPU_OFF
but it is not handled anywhere in the code.

I think you have mixed up the defaults of the configuration and settings 
of igfx_off and intgpu_off somehow which sets something up resulting in 
a wrong config for my boot. intgpu_off boot config itself doesn't change 
anything, with the Debian kernel I need igfx_off.

At
  
https://salsa.debian.org/kernel-team/linux/-/blob/bullseye-security/debian/patches/features/x86/intel-iommu-add-option-to-exclude-integrated-gpu-only.patch#L66
you should compare 10 chars and not only 8, but is more or less 
correctness.

Maybe this
  static int dmar_map_intgpu = 
IS_ENABLED(CONFIG_INTEL_IOMMU_DEFAULT_ON);
at
  
https://salsa.debian.org/kernel-team/linux/-/blob/bullseye-security/debian/patches/features/x86/intel-iommu-add-kconfig-option-to-exclude-igpu-by-default.patch#L74
should be
  static int dmar_map_intgpu = 
IS_ENABLED(INTEL_IOMMU_DEFAULT_ON_INTGPU_OFF);
or the negated value, not sure at the moment, what a y or n should mean 
in this config and if the assignments of 0 or 1 are correct everywhere.

Attachment: bug-1012210-kernel-logs.tar.xz
Description: application/xz