Re: [PATCH RFC v6 11/18] riscv_cbqri: resctrl: Add cache allocation via capacity block mask

[Drew Fustini <fustini@kernel.org>]

On Mon, Jun 01, 2026 at 08:56:08PM +0000, sashiko-bot@kernel.org wrote:
> > @@ -595,6 +595,7 @@ config RISCV_ISA_SSQOSID
> >  	bool "Ssqosid extension support for supervisor mode Quality of Service ID"
> >  	depends on 64BIT
> >  	default n
> > +	select ARCH_HAS_CPU_RESCTRL
> 
> Does selecting ARCH_HAS_CPU_RESCTRL here unconditionally allow RESCTRL_FS
> to be enabled, even if the RISC-V backend driver isn't built?
> 
> Since the backend implementation in cbqri_resctrl.c is gated by
> RISCV_CBQRI_DRIVER:
> 
> config RISCV_CBQRI_RESCTRL_FS
>     bool
>     default y if RISCV_CBQRI_DRIVER && RESCTRL_FS
> 
> Could this result in a linker error for missing resctrl_arch_* symbols if
> RISCV_ISA_SSQOSID is enabled but RISCV_CBQRI_DRIVER is disabled?

This is not reachable. RESCTRL_FS cannot be enabled without the backend that provides the resctrl_arch_* symbols.

> > +		cbqri_res = &cbqri_resctrl_resources[rid];
> > +		if (cbqri_res->ctrl) {
> > +			/*
> > +			 * CCs at the same cache level must agree on every cap
> > +			 * resctrl exposes globally. Reject mismatches at pick
> > +			 * time so the inconsistency is visible at boot.
> > +			 */
> > +			if (cbqri_res->ctrl->rcid_count != ctrl->rcid_count ||
> > +			    cbqri_res->ctrl->cc.ncblks != ctrl->cc.ncblks ||
> > +			    cbqri_res->ctrl->cc.supports_alloc_at_code !=
> > +				    ctrl->cc.supports_alloc_at_code ||
> > +			    cbqri_res->ctrl->alloc_capable != ctrl->alloc_capable) {
> 
> Is this alloc_capable mismatch check dead code?
> 
> Because the earlier loop condition explicitly skips controllers where
> alloc_capable is false:
> 
>     if (!ctrl->alloc_capable) {
>         ...
>         continue;
>     }
> 
> Will both cbqri_res->ctrl and the current ctrl always have alloc_capable
> set to true at this point in cbqri_resctrl_pick_caches? This seems to
> cause non-alloc-capable controllers to be silently ignored rather than
> triggering the fatal configuration error described in the commit message.

It is harmless, but I will drop the dead term in v7 for clarity.

Drew