From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexander Graf Subject: Re: [PATCH 1/4] KVM: PPC: BOOK3S: PR: Emulate virtual timebase register Date: Fri, 06 Jun 2014 00:36:12 +0200 Message-ID: <5390F0DC.9070103@suse.de> References: <1401970085-14493-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <1401970085-14493-2-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <5390604C.4050704@suse.de> <87wqcvmk3f.fsf@linux.vnet.ibm.com> <5390A071.9040006@suse.de> <87sinjqn1g.fsf@linux.vnet.ibm.com> <5390EFF6.50504@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: linuxppc-dev@lists.ozlabs.org, kvm-ppc@vger.kernel.org, kvm@vger.kernel.org To: "Aneesh Kumar K.V" , benh@kernel.crashing.org, paulus@samba.org Return-path: In-Reply-To: <5390EFF6.50504@suse.de> Sender: kvm-ppc-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 06.06.14 00:32, Alexander Graf wrote: > > On 05.06.14 19:33, Aneesh Kumar K.V wrote: >> Alexander Graf writes: >> >>> On 05.06.14 17:50, Aneesh Kumar K.V wrote: >>>> Alexander Graf writes: >>>> >>>>> On 05.06.14 14:08, Aneesh Kumar K.V wrote: >>>>>> virtual time base register is a per VM, per cpu register that needs >>>>>> to be saved and restored on vm exit and entry. Writing to VTB is not >>>>>> allowed in the privileged mode. >>>>>> >>>>>> Signed-off-by: Aneesh Kumar K.V >> ....... >> >>>>>> break; >>>>>> diff --git a/arch/powerpc/kvm/book3s_emulate.c >>>>>> b/arch/powerpc/kvm/book3s_emulate.c >>>>>> index 3565e775b61b..1bb16a59dcbc 100644 >>>>>> --- a/arch/powerpc/kvm/book3s_emulate.c >>>>>> +++ b/arch/powerpc/kvm/book3s_emulate.c >>>>>> @@ -577,6 +577,9 @@ int kvmppc_core_emulate_mfspr_pr(struct >>>>>> kvm_vcpu *vcpu, int sprn, ulong *spr_val >>>>>> */ >>>>>> *spr_val = vcpu->arch.spurr; >>>>>> break; >>>>>> + case SPRN_VTB: >>>>>> + *spr_val = vcpu->arch.vtb; >>>>> Doesn't this mean that vtb can be the same 2 when the guest reads >>>>> it 2 >>>>> times in a row without getting preempted? >>>> But a mfspr will result in VM exit and that would make sure we >>>> update vcpu->arch.vtb with the correct value. >>> We only call kvmppc_core_vcpu_put_pr() when we context switch away from >>> KVM, so it won't be updated, no? >>> >>> >> kvmppc_copy_from_svcpu is also called from VM exit path >> (book3s_interrupt.S) > > ... where it will run into this code path: > > /* > * Maybe we were already preempted and synced the svcpu from > * our preempt notifiers. Don't bother touching this svcpu then. > */ > if (!svcpu->in_use) > goto out; Scratch that. We're always calling this on entry/exit, so you're right. Alex