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

On 2/17/26 3:56 PM, Christian Zigotzky wrote:

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On 17/02/26 11:17 Madhavan Srinivasan wrote:

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On 2/17/26 3:14 PM, Christian Zigotzky wrote:

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On 17/02/26 10:03, Shrikanth Hegde wrote:

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On 2/17/26 2:22 PM, Christian Zigotzky wrote:

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Hi,

Thank you for your patch. I tested the latest git kernel with 
your patch today. Unfortunately the system freezes while booting 
the VM with KVM HV.

Cheers,
Christian

Would it be possible to share the console log or boot log of KVM 
to the
point it freezes?

Unfortunately there aren't any error messages.

I also tried it with:

gdb --args qemu-system-ppc64 -M ppce500 -cpu e5500 -m 1024 -kernel 
uImage-7.0-preempt -drive 
format=raw,file=void-live-powerpc-20230317- 
updated2.img,index=0,if=virtio -netdev user,id=mynet0 -device 
virtio- net,netdev=mynet0 -append "rw root=/dev/vda" -device 
virtio-gpu-pci - device virtio-mouse-pci -device 
virtio-keyboard-pci -enable-kvm -smp 4

and with gdb in the guest:

qemu-system-ppc64 -s -S -M ppce500 -cpu e5500 -m 1024 -kernel 
uImage-7.0-preempt -drive 
format=raw,file=void-live-powerpc-20230317- 
updated2.img,index=0,if=virtio -netdev user,id=mynet0 -device 
virtio- net,netdev=mynet0 -append "rw root=/dev/vda" -device 
virtio-gpu-pci - device virtio-mouse-pci -device 
virtio-keyboard-pci -enable-kvm -smp 4

The system freezed without any error messages.

Anything on host console?

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can you please share the config.
I tried kvm-hv in my power8/power9 and seems to boot fine without 
any issues with today's upstream
Maddy

Here are the configs.

With PREEMPT: https://github.com/chzigotzky/kernels/blob/ 
d50d259ca63dd2b3b9a9eaabc82e5cc69c8cc9f0/configs/e5500_defconfig

Without PREEMPT: https://github.com/chzigotzky/kernels/blob/main/ 
configs/e5500_defconfig

- Christian

I looked at the code. there was one more place where cond_resched was 
there.

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;
         }