From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sasha Levin Subject: Re: [PATCH v2 1/2] KVM: MMIO: Lock coalesced device when checking for available entry Date: Mon, 18 Jul 2011 13:15:51 +0300 Message-ID: <1310984151.8209.7.camel@lappy> References: <1310729869-1451-1-git-send-email-levinsasha928@gmail.com> <4E23EACD.1020407@redhat.com> <1310981389.8209.3.camel@lappy> <4E2401E6.8020200@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, Ingo Molnar , Marcelo Tosatti , Pekka Enberg To: Avi Kivity Return-path: Received: from mail-ww0-f44.google.com ([74.125.82.44]:50037 "EHLO mail-ww0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753787Ab1GRKQI (ORCPT ); Mon, 18 Jul 2011 06:16:08 -0400 Received: by mail-ww0-f44.google.com with SMTP id 5so3026360wwe.1 for ; Mon, 18 Jul 2011 03:16:07 -0700 (PDT) In-Reply-To: <4E2401E6.8020200@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Mon, 2011-07-18 at 12:50 +0300, Avi Kivity wrote: > On 07/18/2011 12:29 PM, Sasha Levin wrote: > > > Hmm. This means we take the lock for every I/O, whether it hits > > > coalesced mmio or not. > > > > > > We need to do the range check before taking the lock and the space check > > > after taking the lock. > > > > > > > I'll fix that. > > > > Shouldn't the range check be also locked somehow? Currently it is > > possible that a coalesced region was removed while we are checking the > > ranges, and we won't issue a mmio exit as the host expects > > It's "locked" using rcu. > Where is that happening? All the coalesced zones are stored under the coalesced "device" in a simple array. When adding and removing zones, kvm->slots_lock is taken - I don't see anything which prevents a range check during zone removal unless slots_lock prevents IO. -- Sasha.