From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de (cantor2.suse.de [195.135.220.15]) (using TLSv1 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 24BA31A0008 for ; Fri, 6 Jun 2014 08:32:47 +1000 (EST) Message-ID: <5390EFF6.50504@suse.de> Date: Fri, 06 Jun 2014 00:32:22 +0200 From: Alexander Graf MIME-Version: 1.0 To: "Aneesh Kumar K.V" , benh@kernel.crashing.org, paulus@samba.org Subject: Re: [PATCH 1/4] KVM: PPC: BOOK3S: PR: Emulate virtual timebase register 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> In-Reply-To: <87sinjqn1g.fsf@linux.vnet.ibm.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Cc: linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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; Alex