From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: [PATCH 2/2] KVM: make guest mode entry to be rcu quiescent state Date: Tue, 3 May 2011 12:42:41 -0300 Message-ID: <20110503154240.GA6898@amt.cnet> References: <1303984323-3203-1-git-send-email-gleb@redhat.com> <1303984323-3203-3-git-send-email-gleb@redhat.com> <20110503131317.GA4244@amt.cnet> <20110503132123.GV2265@redhat.com> <20110503132952.GA5022@amt.cnet> <20110503133901.GW2265@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-kernel@vger.kernel.org, paulmck@linux.vnet.ibm.com, avi@redhat.com, kvm@vger.kernel.org To: Gleb Natapov Return-path: Content-Disposition: inline In-Reply-To: <20110503133901.GW2265@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Tue, May 03, 2011 at 04:39:01PM +0300, Gleb Natapov wrote: > > > > On Thu, Apr 28, 2011 at 12:52:03PM +0300, Gleb Natapov wrote: > > > > > KVM does not hold any references to rcu protected data when it switches > > > > > CPU into a guest mode. In fact switching to a guest mode is very similar > > > > > to exiting to userspase from rcu point of view. In addition CPU may stay > > > > > in a guest mode for quite a long time (up to one time slice). Lets treat > > > > > guest mode as quiescent state, just like we do with user-mode execution. > > > > > > > > > > Signed-off-by: Gleb Natapov > > > > > --- > > > > > include/linux/kvm_host.h | 1 + > > > > > 1 files changed, 1 insertions(+), 0 deletions(-) > > > > > > > > > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > > > > > index 0bc3d37..a347bce 100644 > > > > > --- a/include/linux/kvm_host.h > > > > > +++ b/include/linux/kvm_host.h > > > > > @@ -593,6 +593,7 @@ static inline void kvm_guest_enter(void) > > > > > { > > > > > account_system_vtime(current); > > > > > current->flags |= PF_VCPU; > > > > > + rcu_note_context_switch(smp_processor_id()); > > > > > } > > > > > > > > > > static inline void kvm_guest_exit(void) > > > > > -- > > > > > 1.7.2.3 > > > > > > > > Please have it in x86's vcpu_enter_guest, then its more explicit > > > > (uncertain about the context of kvm_guest_enter call in other arches). > > > > > > > I checked all of them and kvm_guest_enter() is always called with local > > > irq disabled. Paul confirmed that rcu_note_context_switch() can be > > > called in such context. > > > > OK then. Perhaps have an assert to verify interrupts are disabled? > Yes. Can add BUG_ON(preemptible()). Also please add a comment to explain whats going on. The commit message above seems appropriate.