Comment # 12 on bug 1199661 from B

(In reply to Takashi Iwai from comment #10)
> The options can't be set in /etc/modules-load.d/*.conf files but rather in
> /etc/modprobe.d/*.conf file.  The former can contain only the module file
> names to be loaded.
> 
> That is, you'll have to create two files,
> /etc/modules-load.d/amd-pstate.conf containing
>   amd_pstate
> and /etc/modprobe.d/amd-pstate.conf containing
>   options amd-pstate shared_mem=1
> 
> The latter file may contain the blacklist, too.
>   blacklist acpi_cpufreq
> 
> If those modules are to be included in initrd, rebuild initrd.

Kernel 5.18.11 has broken the amd_pstate driver, or the method described here
no longer applies, and it no longer works.