Re: [PATCH] x86/platform: Consider PTM for exposing package-related MSR

[Jan Beulich <jbeulich@xxxxxxxx>]

On 16.02.2026 16:09, Teddy Astie wrote:
> Package-related MSR is actually gated behind "PTM" CPUID flag rather than
> "DTS" one. Make sure we check the right CPUID for package-related MSR.
> 
> Check for either DTS or PTM for MSR_TEMPERATURE_TARGET.
> 
> The only visible difference in practice would be that EPERM would now
> be reported instead of EFAULT if we tried accessing the package MSR on
> a platform that doesn't have it.
> 
> Amends: 615c9f3f820 ("x86/platform: Expose DTS sensors MSR")

Imo this really addresses a bug, so wants to be Fixes:.

> --- a/xen/arch/x86/platform_hypercall.c
> +++ b/xen/arch/x86/platform_hypercall.c
> @@ -89,9 +89,12 @@ static bool msr_read_allowed(unsigned int msr)
>          return cpu_has_srbds_ctrl;
>  
>      case MSR_IA32_THERM_STATUS:
> +        return host_cpu_policy.basic.digital_temp_sensor;

As per the SDM this doesn't look right either - it's CPUID.01H:EDX[22]
(acpi) instead. It is the field you're after in xenpm which is tied to
CPUID.06H:EAX[0] (digital_temp_sensor).

>      case MSR_TEMPERATURE_TARGET:
> +        return host_cpu_policy.basic.digital_temp_sensor ||
> +               host_cpu_policy.basic.package_therm_management;

Where in the SDM did you find this connection? (Anything made up wants
commenting upon.)

>      case MSR_PACKAGE_THERM_STATUS:
> -        return host_cpu_policy.basic.digital_temp_sensor;
> +        return host_cpu_policy.basic.package_therm_management;
>      }

And of course with this splitting of cases, blank lines want inserting
between the case blocks.

> --- a/xen/include/xen/lib/x86/cpu-policy.h
> +++ b/xen/include/xen/lib/x86/cpu-policy.h
> @@ -132,7 +132,7 @@ struct cpu_policy
>                          :1,
>                          :1,
>                          :1,
> -                        :1,
> +                        package_therm_management:1,

The SDM calls this PKG_THERM_MGMT; I think our naming would better match now
that we decided to have everything else here named according to the SDM.

Jan