Re: [RESEND PATCH v4 01/15] x86/resctrl: Support Privilege Level Zero Association (PLZA)

[Borislav Petkov]

On Tue, Jul 07, 2026 at 04:50:02PM -0500, Babu Moger wrote:
> Customers have identified an issue while using the QoS resource control

Please drop the "customers" speak from kernel code.

> feature. If 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 association to be changed during the
> transition from user mode to kernel mode. This allows the kernel to run
> using a different CLOSID than user space, which can improve system
> performance in certain scenarios.
> 
> 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
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=206537 # [2]
> Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
> ---
> v4: Split the patch into 2. This patch only handles x86 changes.
>     Re-wrote the changelog along the ABMC changes.
> 
> v3: Code did not change. Patch order changed.
>     Added documentation link.
> 
> v2: Rebased on top of the latest tip.
> ---
>  arch/x86/include/asm/cpufeatures.h | 1 +
>  arch/x86/kernel/cpu/scattered.c    | 1 +
>  2 files changed, 2 insertions(+)

With that addressed:

Acked-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>

-- 
Regards/Gruss,
    Boris.

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