Re: [PATCH v3 2/2] KVM: selftests: Create one VM with many vCPUs for each major PMU counters test

On Tue, Aug 04, 2026, [email protected] wrote:
> Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:
> > +	pr_info("Testing arch events, PMU version %u, perf_caps = %lx\n",
> > +		pmu_version, perf_capabilities);
> > +
> > +	/* Testing arch events requires a vPMU (there are no negative tests). */
> > +	if (!pmu_version)
> > +		return;
> > +
> > +	vm = pmu_vm_create_with_vcpus((NR_INTEL_ARCH_EVENTS + 2) * (ARRAY_SIZE(unavailable_masks) - 1),
> > +				      guest_test_arch_events, pmu_version,
> > +				      perf_capabilities, &vcpus);
> 
> [Severity: Medium]
> Could this cause the test to assert on hosts with lower vCPU limits?
> 
> This calculation requests up to 144 vCPUs per VM ((14 + 2) * (10 - 1)). If the 
> host has a KVM_CAP_MAX_VCPUS limit lower than 144 (which is common in nested
> virtualization or lightweight VMs), 

No, it's not.  Unless userspace overwrites the VM's max vCPUs, KVM x86's *minimum*
value for KVM_CAP_MAX_VCPUS is 1024.

	case KVM_CAP_MAX_VCPUS:
		r = KVM_MAX_VCPUS;
		if (kvm)
			r = kvm->max_vcpus;
		break;

  #ifdef CONFIG_KVM_MAX_NR_VCPUS
  #define KVM_MAX_VCPUS CONFIG_KVM_MAX_NR_VCPUS
  #else
  #define KVM_MAX_VCPUS 1024
  #endif


  config KVM_MAX_NR_VCPUS
	int "Maximum number of vCPUs per KVM guest"
	depends on KVM_X86
	range 1024 4096
	default 4096 if MAXSMP
	default 1024


KVM_CAP_NR_VCPUS incorporates the number of CPUs in the system, but that's purely
a "suggestion" for userspace.

	case KVM_CAP_NR_VCPUS:
		r = min_t(unsigned int, num_online_cpus(), KVM_MAX_VCPUS);
		break;

> vm_create_with_vcpus() might fail with a hard assertion.
> 
> Should this check against the host limit and either skip via TEST_REQUIRE()
> or batch the creations into smaller groups of vCPUs?