Re: [Linux PPC] Disable PREEMPT

On 04 September 2026 at 10:56 Christian Zigotzky [off-list ref] wrote:

On 03 September 2026 at 07:23 Shrikanth Hegde [off-list ref] wrote:

Friendly LLM analysis says preemption is enabled too early and before
completing kvmppc_handle_exit_hv() / kvmppc_handle_nested_exit()

Below is ONLY a speculation and completely UNTESTED.
Maybe worth a try.

---

diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 0409ac9e7b31..78d2b0618887 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c

@@ -5049,8 +5049,6 @@ int kvmhv_run_single_vcpu(struct kvm_vcpu *vcpu, u64 time_limit,

      powerpc_local_irq_pmu_restore(flags);

-       preempt_enable();
-
      /*
       * cancel pending decrementer exception if DEC is now positive, or if
       * entering a nested guest in which case the decrementer is now owned

@@ -5072,6 +5070,8 @@ int kvmhv_run_single_vcpu(struct kvm_vcpu *vcpu, u64 time_limit,
      }
      vcpu->arch.ret = r;

+       preempt_enable();
+
      if (is_kvmppc_resume_guest(r) && !kvmppc_vcpu_check_block(vcpu)) {
              kvmppc_set_timer(vcpu);

Michal

- - -

Michal,