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Fri, 4 Sep 2026 10:56:05 +0200 (CEST) Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable From: Christian Zigotzky X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list Mime-Version: 1.0 (1.0) Subject: Re: [Linux PPC] Disable PREEMPT Date: Fri, 4 Sep 2026 10:55:54 +0200 Message-Id: References: <5ed38c3e-4aaa-4a91-9eda-e31d09b44abc@linux.ibm.com> Cc: =?utf-8?Q?Michal_Such=C3=A1nek?= , Christophe Leroy , linuxppc-dev , kvm-ppc@vger.kernel.org, Madhavan Srinivasan , Peter Zijlstra , "R.T.Dickinson" , hypexed@yahoo.com.au, mad skateman , Christian Zigotzky In-Reply-To: <5ed38c3e-4aaa-4a91-9eda-e31d09b44abc@linux.ibm.com> To: Shrikanth Hegde X-Mailer: iPhone Mail (23G83) On 03 September 2026 at 07:23 Shrikanth Hegde wrote:= =EF=BB=BFFriendly LLM analysis says preemption is enabled too early and befo= re 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 t= ime_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 t= ime_limit, } vcpu->arch.ret =3D 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 activ= ated? 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=