Broken build when `CONFIG_X86_PAT` is not defined

NVIDIA Open GPU Kernel Modules Version

7c345b838b8a63126ed425781400c1ae8a7a4a1d

Operating System and Version

Ubuntu 22.04.1 LTS

Kernel Release

v5.16.0, custom configured

Build Command

make SYSSRC="/path/to/custom/kernel"

Terminal output/Build Log

$ make SYSSRC="/path/to/custom/kernel"
...
/cache/build/default-deepsea1-6/julia-computing-1/xtrx-julia/software/nvidia-driver/kernel-open/nvidia/nv-pat.c: In function ‘nv_disable_caches’:
/cache/build/default-deepsea1-6/julia-computing-1/xtrx-julia/software/nvidia-driver/kernel-open/nvidia/nv-pat.c:66:5: error: implicit declaration of function ‘__flush_tlb’; did you mean ‘__flush_tlb_all’? [-Werror=implicit-function-declaration]
   66 |     __flush_tlb();
      |     ^~~~~~~~~~~
      |     __flush_tlb_all

More Info

When compiling against a linux kernel without CONFIG_X86_PAT, this conditional enables code that uses __flush_tlb(). This function was, if I am reading the kernel source correctly, removed in Linux 5.8. This codepath should be updated to no longer use the outdated function on newer Linux kernel versions.

Start in kernel-open/nvidia/nv-pat.c around the CONFIG_X86_PAT conditional and the nv_disable_caches call shown in the build log. Compare the referenced Linux 5.8 change with the custom kernel headers, then build with CONFIG_X86_PAT unset using the reported make command. Done means this configuration no longer fails on the outdated __flush_tlb declaration.