Re: 6.1 Backport request: fbf5892df21a ("kbuild: Use CRC32 and a 1MiB dictionary for XZ compressed modules")

[Greg KH <greg@kroah.com>]

On Thu, Dec 25, 2025 at 11:48:03AM +0100, Christoph Biedl wrote:
> Hello,
> 
> please backport
> 
> commit fbf5892df21a8ccfcb2fda0fd65bc3169c89ed28
> Author: Martin Nybo Andersen <tweek@tweek.dk>
> Date:   Fri Sep 15 12:15:39 2023 +0200
> 
>     kbuild: Use CRC32 and a 1MiB dictionary for XZ compressed modules
> 
>     Kmod is now (since kmod commit 09c9f8c5df04 ("libkmod: Use kernel
>     decompression when available")) using the kernel decompressor, when
>     loading compressed modules.
> 
>     However, the kernel XZ decompressor is XZ Embedded, which doesn't
>     handle CRC64 and dictionaries larger than 1MiB.
> 
>     Use CRC32 and 1MiB dictionary when XZ compressing and installing
>     kernel modules.
> 
> to the 6.1 stable kernel, and possibly older ones as well.
> 
> The commit message actually has it all, so just my story: There's a
> hardware that has or had issues with never kernels (no time to check),
> my kernel for this board is usually static. But after building a kernel
> with xz-compressed modules, they wouldn't load but trigger
> "decompression failed with status 6". Investigation led to a CRC64 check
> for these files, and eventually to the above commit.
> 
> The commit applies (with an offset), the resulting modules work as
> expected.
> 
> Kernel 6.6 and newer already have that commit. Older kernels could
> possibly benefit from this as well, I haven't checked.

Now queued up, thanks.

greg k-h