Re: [RFC PATCH 13/19] x86/resctrl: Add PLZA state tracking and context switch handling

[Drew Fustini <fustini@kernel.org>]

On Thu, Feb 19, 2026 at 09:03:20AM -0800, Luck, Tony wrote:
> > Likely real implementation:
> > 
> > Sub-components of each of the ideas above are encoded as a bitmask that
> > is written to plza_mode. There is a file in the info/ directory listing
> > which bits are supported on the current system (e.g. the "keep the same
> > RMID" mode may be impractical on ARM, so it would not be listed as an
> > option.)
> 
> 
> In x86 terms where control and monitor functions are independent we
> have:
> 
> Control:
> 1) Use default (CLOSID==0) for kernel
> 2) Allocate just one CLOSID for kernel
> 3) Allocate many CLOSIDs for kernel
> 
> Monitor:
> 1) Do not monitor kernel separately from user
> 2) Use default (RMID==0) for kernel
> 3) Allocate one RMID for kernel
> 4) Allocate many RMIDs for kernel
> 
> What options are possible on ARM & RISC-V?

The RISC-V Ssqosid extension just adds one register to each processor
which contains a single resource control id (rcid) and a single
monitoring control id (mcid). Any switching of rcid or mcid between
kernel mode and user mode would need to be done manually by the kernel
on entry/exit.

Thanks,
Drew