From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paul Mackerras Subject: Re: [PATCH] KVM: PPC: BOOK3S: PR: Fix PURR and SPURR emulation Date: Wed, 4 Jun 2014 14:15:47 +1000 Message-ID: <20140604041547.GA32223@drongo> References: <1401797771-25606-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: agraf@suse.de, benh@kernel.crashing.org, linuxppc-dev@lists.ozlabs.org, kvm-ppc@vger.kernel.org, kvm@vger.kernel.org To: "Aneesh Kumar K.V" Return-path: Content-Disposition: inline In-Reply-To: <1401797771-25606-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> Sender: kvm-ppc-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Tue, Jun 03, 2014 at 05:46:11PM +0530, Aneesh Kumar K.V wrote: > We use time base for PURR and SPURR emulation with PR KVM since we > are emulating a single threaded core. When using time base > we need to make sure that we don't accumulate time spent in the host > in PURR and SPURR value. Mostly looks good except for this... > @@ -170,6 +175,11 @@ void kvmppc_copy_from_svcpu(struct kvm_vcpu *vcpu, > > out: > preempt_enable(); > + /* > + * Update purr and spurr using time base > + */ > + vcpu->arch.purr += get_tb() - vcpu->arch.entry_tb; > + vcpu->arch.spurr += get_tb() - vcpu->arch.entry_tb; You need to do those updates before the "out:" label. Otherwise if this function gets called with !svcpu->in_use (which can happen if CONFIG_PREEMPT is enabled) we would do these updates a second time for one guest exit. The thing is that kvmppc_copy_from_svcpu() can get called from kvmppc_core_vcpu_put_pr() if the vcpu task gets preempted on the way out from the guest before we get to the regular call of kvmppc_copy_from_svcpu(). It would then get called again when the task gets to run, but this time it does nothing because svcpu->in_use is false. Paul.