Re: [Linux PPC] Disable PREEMPT
From: Christian Zigotzky <hidden>
Date: 2026-09-04 08:56:25
Subsystem:
kernel virtual machine for powerpc (kvm/powerpc), linux for powerpc (32-bit and 64-bit), the rest · Maintainers:
Madhavan Srinivasan, Linus Torvalds
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, Is this patch also for the issues with KVM PR and KVM HV if PREEMPT is activated? The entire FSL Cyrus+ board freezes when using KVM HV with PREEMPT. The guest kernel doesn't boot if we use KVM PR with a PREEMPT kernel on the PA Semi Nemo board. Bug report: https://github.com/chzigotzky/kernels/issues/19 Thanks, Christian