Re: [PATCH v8 11/20] KVM: selftests: Verify interrupts are received when IRQ affinity changes in IRQ test

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The IRQ affinity logic incorrectly assumes that CPU IDs are contiguous and zero-indexed up to `get_nprocs() - 1`, which will cause spurious test crashes on systems with sparse CPU topologies or offline CPUs.
--

commit 907b9a0cf2f427a532d2facb5d6393850a4b6083
Author: David Matlack <dmatlack@google.com>

KVM: selftests: Verify interrupts are received when IRQ affinity changes in IRQ test

This commit extends the KVM eventfd IRQ selftest with a '-a' flag. This flag
randomly affinitizes the device's host IRQ to different physical CPUs to
stress KVM's interrupt routing logic while affinity changes dynamically.

> diff --git a/tools/testing/selftests/kvm/irq_test.c b/tools/testing/selftests/kvm/irq_test.c
> index 70b2c9cac2790..fd386e3e9ac3e 100644
> --- a/tools/testing/selftests/kvm/irq_test.c
> +++ b/tools/testing/selftests/kvm/irq_test.c

[ ... ]

> @@ -228,6 +239,11 @@ int main(int argc, char **argv)
>  
>  		kvm_route_msi(vm, gsi, vcpu, vector);
>  
> +		if (irq_affinity) {
> +			irq_cpu = kvm_random_u64(&kvm_rng) % get_nprocs();
> +			proc_irq_set_smp_affinity(irq, irq_cpu);

[Severity: Medium]
Will this cause spurious test crashes on systems with non-contiguous CPU IDs
or offline CPUs?

Since get_nprocs() returns the count of currently online processors, using it
with a modulo operation in main() assumes that the online CPU IDs are
contiguous and start from 0. On a system where CPUs are offline or the
numbering is sparse (for example, if only CPUs 0 and 2 are online,
get_nprocs() returns 2, and the modulo yields 0 or 1), this could select an
offline or non-existent CPU ID.

Attempting to write an invalid CPU ID to /proc/irq/<irq>/smp_affinity_list
via proc_irq_set_smp_affinity() would then fail with -EINVAL and erroneously
crash the test.

> +		}
> +
>  		for (j = 0; j < nr_vcpus; j++)

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260626213534.3866178-1-seanjc@google.com?part=11