Re: [PATCH v5 19/21] KVM: selftests: Print vCPU affinity on timeout during IRQ test

[Sean Christopherson <seanjc@google.com>]

On Thu, Jun 04, 2026, sashiko-bot@kernel.org wrote:
> > +void kvm_print_vcpu_affinity(struct kvm_vcpu *vcpu, pid_t tid)
> > +{
> > +	int nprocs = get_nprocs();
> > +	bool first_range = true;
> > +	int i, start = -1;
> > +	cpu_set_t cpus;
> > +
> > +	kvm_sched_getaffinity(tid, sizeof(cpus), &cpus);
> > +
> > +	/*
> > +	 * Output format examples:
> > +	 * - Single CPU:  "vCPU 0 (TID 1234) affined to pCPU(s): 2"
> > +	 * - List:        "vCPU 0 (TID 1234) affined to pCPU(s): 0,2,4"
> > +	 * - Range:       "vCPU 0 (TID 1234) affined to pCPU(s): 0-7"
> > +	 * - Mixed:       "vCPU 0 (TID 1234) affined to pCPU(s): 0-3,8,10-12"
> > +	 */
> > +	printf("vCPU %u (TID %d) affined to pCPU(s): ", vcpu->id, tid);
> > +
> > +	for (i = 0; i <= nprocs; i++) {
> > +		/*
> > +		 * Iterate to nprocs (inclusive) to ensure that if the last pCPU
> > +		 * is part of a range, the 'else' block triggers one final time
> > +		 * to flush that range to stdout.
> > +		 */
> > +		if (i < nprocs && CPU_ISSET(i, &cpus)) {
> 
> [Severity: Medium]
> Does using get_nprocs() as the loop boundary risk silently truncating CPUs 
> on sparse topologies?
> 
> get_nprocs() returns the count of currently online CPUs, not the maximum 
> CPU ID. If a system has 4 online CPUs but their IDs are 0, 1, 2, and 7, 
> get_nprocs() will return 4.
> 
> This would cause the loop to terminate prematurely, completely ignoring 
> valid but higher-numbered CPU indices (like CPU 7) in the cpu_set_t mask.
> 
> Should this iterate up to CPU_SETSIZE instead to encompass the entire mask 
> capacity, similar to other helper functions like pin_task_to_random_cpu()?

I'm going to skip this one for now, too.