From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Aneesh Kumar K.V" Subject: Re: [PATCH 1/4] KVM: PPC: BOOK3S: PR: Emulate virtual timebase register Date: Thu, 05 Jun 2014 23:03:15 +0530 Message-ID: <87sinjqn1g.fsf@linux.vnet.ibm.com> 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> Mime-Version: 1.0 Content-Type: text/plain Cc: linuxppc-dev@lists.ozlabs.org, kvm-ppc@vger.kernel.org, kvm@vger.kernel.org To: Alexander Graf , benh@kernel.crashing.org, paulus@samba.org Return-path: In-Reply-To: <5390A071.9040006@suse.de> Sender: kvm-ppc-owner@vger.kernel.org List-Id: kvm.vger.kernel.org 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) -aneesh