Re: [PATCH v6 03/18] x86/resctrl: Add PLZA configuration definitions and data structures

[Babu Moger]

Hi Reinette,

On 10/19/26 11:16, Reinette Chatre wrote:
> Hi Babu,
>
> On 10/15/26 4:07 PM, Babu Moger wrote:
> > On 10/15/26 09:22, Reinette Chatre wrote:
> > > On 10/1/26 8:10 AM, Babu Moger wrote:
> > > > Privilege Level Zero Association (PLZA) enables the kernel to switch to
> > > > a different CLOSID and/or RMID than those used in user mode when entering
> > > > kernel mode. CLOSID and RMID selection are independent and can be
> > > > configured separately.
> > >
> > > That CLOSID and RMID are independent on x86 is clear to me. That they can be
> > > configured separately is not clear to me in this context. What does this
> > > "separate configuration" refer to? Looking at the later patches kernel
> > > mode allocation and monitoring associations are always configured together
> > > and written to same MSR at the same time?
> >
> >
> > Good point. Its confusing.  What I meant is that allocation (CLOSID)
> > and monitoring (RMID) associations are independent PLZA features and
> > can be enabled independently in hardware. For example, a platform
> > may enable kernel mode CLOSID association without enabling kernel
> > mode RMID association, or vice versa.
> >
> > Yes. The kernel interface configures both together because they are carried in the same IA32_PQR_ASSOC MSR update.
> >
> > How about?
> >
> > Privilege Level Zero Association (PLZA) enables the kernel to use a
> > different CLOSID and/or RMID in kernel mode than in user mode.
> > Allocation (CLOSID) and monitoring (RMID) associations are
> > independent PLZA features and may be enabled independently by
> > hardware.
>
> Which CLOSID (MSR_IA32_PQR_PLZA_ASSOC.closid) and/or RMID (MSR_IA32_PQR_PLZA_ASSOC.rmid)
> is used in kernel mode is different from whether the CLOSID (MSR_IA32_PQR_PLZA_ASSOC.closid_en)
> and/or RMID (MSR_IA32_PQR_PLZA_ASSOC.rmid_en) is used in kernel mode.
>
> This series uses the high level "allocation and monitoring association" term
> interchangeably for both of these meanings and doing so causes confusion.
>
> Please pick specific terms to refer to the CLOSID/RMID assigned to kernel mode vs
> whether the CLOSID/RMID assignment is enabled and use it throughout the series.

Another attempt to capture all the details:

"Privilege Level Zero Association (PLZA) enables the kernel to use a 
different CLOSID and/or RMID than those used in user mode when executing 
in kernel mode. CLOSID and RMID selection can be configured independently.

The kernel mode CLOSID and RMID are specified by 
MSR_IA32_PQR_PLZA_ASSOC.closid and MSR_IA32_PQR_PLZA_ASSOC.rmid, 
respectively. plza_en activates the PLZA operation, while closid_en and 
rmid_en independently control whether the corresponding kernel mode 
CLOSID or RMID is used.

Make the register and its field layout available so kernel mode 
allocation (CLOSID) and monitoring (RMID) selection can be configured 
independently."

Thanks
Babu