Re: [PATCH v6 5/8] riscv_cbqri: resctrl: Add cache allocation via capacity block mask

[Drew Fustini <fustini@kernel.org>]

On Thu, Jul 30, 2026 at 01:27:22AM +0000, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] Capacity controllers registered after boot bypass capability validation, which can cause resctrl failures and hardware writes with out-of-bounds parameters.
> --
> 
> --- Patch [5]: [PATCH v6 5/8] riscv_cbqri: resctrl: Add cache allocation via capacity block mask ---
> commit b95a917a4c4e682ec805c748e42c4a7bedae47b2
> Author: Drew Fustini <fustini@kernel.org>
> 
>     riscv_cbqri: resctrl: Add cache allocation via capacity block mask
> 
> This commit wires CBQRI capacity controllers into resctrl as RDT_RESOURCE_L2
> and RDT_RESOURCE_L3 schemata. It handles domain creation during the cpuhp
> online callback for offline CPUs, and defines context-switch and capability
> checks for RISC-V.
> 
> > diff --git a/drivers/resctrl/cbqri_resctrl.c b/drivers/resctrl/cbqri_resctrl.c
> > index 0000000000000..0c4bfa2a7f433
> > --- /dev/null
> > +++ b/drivers/resctrl/cbqri_resctrl.c
> [ ... ]
> > +static int cbqri_attach_cpu_to_all_ctrls(unsigned int cpu)
> > +{
> > +	static const u32 levels[] = { 2, 3 };
> > +	struct cbqri_controller *ctrl, *c;
> > +	struct cbqri_resctrl_res *hw_res;
> > +	struct rdt_ctrl_domain *d;
> > +	struct cacheinfo *ci;
> > +	int i, rid;
> [ ... ]
> > +		/* The controller backing this CPU's cache at this level. */
> > +		ctrl = NULL;
> > +		list_for_each_entry(c, &cbqri_controllers, list) {
> > +			if (c->type == CBQRI_CONTROLLER_TYPE_CAPACITY &&
> > +			    c->alloc_capable &&
> > +			    c->cache.cache_level == levels[i] &&
> > +			    c->cache.cache_id == ci->id) {
> > +				ctrl = c;
> > +				break;
> > +			}
> > +		}
> > +		if (!ctrl)
> > +			continue;
> > +
> > +		d = cbqri_find_ctrl_domain(&hw_res->resctrl_res.ctrl_domains,
> > +					   ci->id);
> > +		if (d) {
> > +			cpumask_set_cpu(cpu, &d->hdr.cpu_mask);
> > +			continue;
> > +		}
> > +
> > +		d = cbqri_create_ctrl_domain(ctrl, &hw_res->resctrl_res, cpu,
> > +					     ci->id);
> 
> [Severity: High]
> Does this code allow a late-registered controller to bypass the capability
> validation?
> 
> During boot, cbqri_resctrl_pick_caches() validates that all controllers at a
> given cache level have identical capabilities (like ncblks and rcid_count)
> using cbqri_cc_caps_agree().
> 
> However, in the CPU hotplug path, if a new cache controller is probed
> after boot, cbqri_attach_cpu_to_all_ctrls() finds it and creates a
> domain without verifying it matches the baseline hw_res->ctrl.

This is not a problem as there is no path that registers a controller
after boot.

Drew