Re: [PATCH] cpufreq/amd-pstate: Bail out early in virtual machines and don't warn

[Mario Limonciello <mario.limonciello@amd.com>]

+Jason
+Boris

On 7/15/26 12:41, Rong Zhang wrote:
> When booting a virtual machine that simulates or passes-through a
> relatively new CPUID, one or two warning messages are printed to kmsg:
> 
>      amd_pstate: The CPPC feature is supported but currently disabled by the BIOS.
>      Please enable it if your BIOS has the CPPC option.
>      amd_pstate: the _CPC object is not present in SBIOS or ACPI disabled
> 
> Technically the check is not wrong and acts as a safetynet that prevents
> the driver from being registered incorrectly, but the warning messages
> are noisy and not really helpful, as virtual machines cannot adjust the
> CPU frequency from the very beginning. Moreover, mentioning BIOS here
> makes the messages even more confusing.
> 
> Fix it by bailing out early when running in virtual machines (excluding
> Xen Dom0).

Conceptually this makes sense to me, but I would like some comments from 
others if this is the right way forward.

Jason, Boris,

comments please?

> 
> Fixes: cb817ec6673b ("cpufreq: amd-pstate: show CPPC debug message if CPPC is not supported")
> Signed-off-by: Rong Zhang <i@rong.moe>
> ---
>   drivers/cpufreq/amd-pstate.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index a74a4cf99d22..f2115f935318 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -2228,6 +2228,9 @@ static int __init amd_pstate_init(void)
>   	if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD)
>   		return -ENODEV;
>   
> +	if (cpu_feature_enabled(X86_FEATURE_HYPERVISOR) && !xen_initial_domain())
> +		return -ENODEV;
> +
>   	/* show debug message only if CPPC is not supported */
>   	if (!amd_cppc_supported())
>   		return -EOPNOTSUPP;
> 
> ---
> base-commit: 58717b2a1365d06c8c64b72aa948541b53fe31eb
> change-id: 1cc24037-amd-pstate-vm-d6ab4c959bd3
> 
> Thanks,
> Rong
>