Re: [PATCH v6 01/18] x86/cpufeatures: Support Privilege Level Zero Association (PLZA)

[Reinette Chatre]

Hi Babu,

On 10/1/26 8:10 AM, Babu Moger wrote:
> When memory bandwidth associated with a CLOSID is aggressively throttled,
> and a task with that CLOSID moves into kernel mode, the kernel operations
> are also aggressively throttled. This can stall forward progress and
> eventually degrade overall system performance.
> 
> AMD hardware supports a feature Privilege Level Zero Association (PLZA),
> which allows the CPU's CLOSID and/or RMID association to be changed during
> the transition from user mode to kernel mode. This allows the kernel to run
> using a different CLOSID and/or RMID than user space, which can improve
> system performance and/or allow kernel work to be monitored separately.
> 
> Note that PLZA feature associates CLOSID and/or RMID to kernel work, and
> therefore influences resource allocation and/or monitoring for all
> resources, not only memory bandwidth.
> 
> The feature is detected via CPUID_Fn80000020_EBX_x00 [Bit 9]: Privilege
> Level Zero Association (PLZA).
> 
> The PLZA feature details are documented in [1] available from [2].
> 
> [1] AMD64 Zen6 Platform Quality of Service (PQOS) Extensions:
>     Publication # 69193 Revision: 1.00, Issue Date: March 2026
> 
> Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
> Acked-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537 # [2]
> ---

Reviewed-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>

Reinette