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

[Babu Moger <babu.moger@amd.com>]

Hi Boris,

On 7/7/26 17:01, Borislav Petkov wrote:
> 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.

Will change the text to:

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.


> 
>> 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@amd.com>
>> ---
>> 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@alien8.de>
> 

Thanks
Babu