From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Dr. David Alan Gilbert" Subject: Re: [PATCH v2 0/4] Balloon inhibit enhancements, vfio restriction Date: Tue, 31 Jul 2018 16:07:46 +0100 Message-ID: <20180731150746.GH2476@work-vm> References: <153299204130.14411.11438396195753743913.stgit@gimli.home> <20180731152716-mutt-send-email-mst@kernel.org> <20180731084414.52e560fa@t450s.home> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: kvm@vger.kernel.org, david@redhat.com, cohuck@redhat.com, qemu-devel@nongnu.org, peterx@redhat.com, "Michael S. Tsirkin" To: Alex Williamson Return-path: Content-Disposition: inline In-Reply-To: <20180731084414.52e560fa@t450s.home> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+gceq-qemu-devel2=m.gmane.org@nongnu.org Sender: "Qemu-devel" List-Id: kvm.vger.kernel.org * Alex Williamson (alex.williamson@redhat.com) wrote: > On Tue, 31 Jul 2018 15:29:17 +0300 > "Michael S. Tsirkin" wrote: > > > On Mon, Jul 30, 2018 at 05:13:26PM -0600, Alex Williamson wrote: > > > v2: > > > - Use atomic ops for balloon inhibit counter (Peter) > > > - Allow endpoint driver opt-in for ballooning, vfio-ccw opt-in by > > > default, vfio-pci opt-in by device option, only allowed for mdev > > > devices, no support added for platform as there are no platform > > > mdev devices. > > > > > > See patch 3/4 for detailed explanation why ballooning and device > > > assignment typically don't mix. If this eventually changes, flags > > > on the iommu info struct or perhaps device info struct can inform > > > us for automatic opt-in. Thanks, > > > > > > Alex > > > > So this patch seems to block ballooning when vfio is added. > > But what if balloon is added and inflated first? > > Good point. > > > I'd suggest making qemu_balloon_inhibit fail in that case, > > and then vfio realize will fail as well. > > That might be the correct behavior for vfio, but I wonder about the > existing postcopy use case. Dave Gilbert, what do you think? We might > need a separate interface for callers that cannot tolerate existing > ballooned pages. Of course we'll also need another atomic counter to > keep a tally of ballooned pages. Thanks, For postcopy, preinflation isn't a problem; our only issue is ballooning during the postcopy phase itself. Dave > Alex -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK