Re: [PATCH v2 06/12] KVM: selftests: Affine threads to random CPUs in hardware disable test

[Sean Christopherson <seanjc@google.com>]

On Fri, Jul 31, 2026, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Medium] Randomly selected CPUs are not removed from `allowed_cpu_set`, leading to duplicate selections and artificially reduced test concurrency.
> --
> 
> --- Patch [6]: [PATCH v2 06/12] KVM: selftests: Affine threads to random CPUs in hardware disable test ---
> commit 093b65b96e15e7cdd5b611bd7d8556fb88cae6e6
> Author: Sean Christopherson <seanjc@google.com>
> 
> KVM: selftests: Affine threads to random CPUs in hardware disable test
> 
> This patch modifies the hardware disable test to affine worker threads
> to random CPUs instead of hardcoding them to CPUs 0-3. It also honors
> the starting CPU set during this process.
> 
> > diff --git a/tools/testing/selftests/kvm/hardware_disable_test.c b/tools/testing/selftests/kvm/hardware_disable_test.c
> > index d8288147b0a69..bd23c13003707 100644
> > --- a/tools/testing/selftests/kvm/hardware_disable_test.c
> > +++ b/tools/testing/selftests/kvm/hardware_disable_test.c
> > @@ -149,12 +149,15 @@ void wait_for_child_setup(pid_t pid)
> >  
> >  int main(int argc, char **argv)
> >  {
> > +	cpu_set_t allowed_cpu_set;
> >  	u32 i;
> >  	int s, r;
> >  	pid_t pid;
> >  
> > -	for (i = 0; i < VCPU_NUM; i++)
> > -		CPU_SET(i, &threads_cpu_set);
> > +	kvm_sched_getaffinity(0, sizeof(cpu_set_t), &allowed_cpu_set);
> > +
> > +	for (i = 0; i < VCPU_NUM && CPU_COUNT(&allowed_cpu_set); i++)
> > +		CPU_SET(kvm_pick_random_cpu(&allowed_cpu_set), &threads_cpu_set);
> 
> [Severity: Medium]
> Since kvm_pick_random_cpu() doesn't clear the selected CPU from
> allowed_cpu_set, can the same CPU be selected multiple times here?

/facepalm

Remembered to CPU_CLR() the selected cpu in all my fancy version, then forgot to
do so for the simple version.