Re: [Linux PPC] KVM PR and KVM HV do not work if the kernel was compiled with PREEMPT

Shrikanth Hegde
2026-02-23T03:45:27Z

Hi Christian.

>> If possible give the below try.
>> (Note: Didn;t replicate your issue)
>>
>> ---
>>
>> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
>> index 7667563fb9ff..bf0ca49c9915 100644
>> --- a/arch/powerpc/kvm/book3s_hv.c
>> +++ b/arch/powerpc/kvm/book3s_hv.c
>> @@ -4825,10 +4825,13 @@ static int kvmppc_run_vcpu(struct kvm_vcpu *vcpu)
>>          vc->runner = vcpu;
>>          if (n_ceded == vc->n_runnable) {
>>              kvmppc_vcore_blocked(vc);
>> -        } else if (need_resched()) {
>> +        } else if (need_resched() || spin_needbreak(&vc->lock)) {
>>              kvmppc_vcore_preempt(vc);
>>              /* Let something else run */
>> -            cond_resched_lock(&vc->lock);
>> +            spin_unlock(&vc->lock);
>> +            schedule();
>> +            //cond_resched_lock(&vc->lock);
>> +            spin_lock(&vc->lock);
>>              if (vc->vcore_state == VCORE_PREEMPT)
>>                  kvmppc_vcore_end_preempt(vc);
>>          } else {
>> @@ -4901,7 +4904,7 @@ int kvmhv_run_single_vcpu(struct kvm_vcpu *vcpu,
>> u64 time_limit,
>>      }
>>
>>      if (need_resched())
>> -        cond_resched();
>> +        schedule();
>>
>>      kvmppc_update_vpas(vcpu);
>>
>> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
>> index 9a89a6d98f97..54963c1d8b58 100644
>> --- a/arch/powerpc/kvm/powerpc.c
>> +++ b/arch/powerpc/kvm/powerpc.c
>> @@ -86,7 +86,7 @@ int kvmppc_prepare_to_enter(struct kvm_vcpu *vcpu)
>>      while (true) {
>>          if (need_resched()) {
>>              local_irq_enable();
>> -            cond_resched();
>> +            schedule();
>>              hard_irq_disable();
>>              continue;
>>          }
>>
> Hello Shrikanth,
> t
> I tested your patch today. The patched preempt kernel boots on my e5500
> host and in an e5500 VM. Unfortunately my guest and host freeze after
> loading the VirtIO-GPU.
>
> Thanks for your help,
>
> Christian

Glad it helps you to boot into.

Since you said even host freezes, host maybe crashing.
Do you have the console log when you load the VirtIO-GPU?