From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37966) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZFdho-0001uk-9h for qemu-devel@nongnu.org; Thu, 16 Jul 2015 03:35:45 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZFdhg-0003sE-TM for qemu-devel@nongnu.org; Thu, 16 Jul 2015 03:35:44 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53337) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZFdhg-0003ry-J5 for qemu-devel@nongnu.org; Thu, 16 Jul 2015 03:35:36 -0400 Date: Thu, 16 Jul 2015 10:35:33 +0300 From: "Michael S. Tsirkin" Message-ID: <20150716103150-mutt-send-email-mst@redhat.com> References: <1436442444-132020-1-git-send-email-imammedo@redhat.com> <20150715171201.05f6bc0d@nial.brq.redhat.com> <20150715192933-mutt-send-email-mst@redhat.com> <20150716092621.5ff1bd40@nial.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150716092621.5ff1bd40@nial.brq.redhat.com> Subject: Re: [Qemu-devel] [PATCH v4 0/7] Fix QEMU crash during memory hotplug with vhost=on List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Igor Mammedov Cc: pbonzini@redhat.com, qemu-devel@nongnu.org, peter.maydell@linaro.org On Thu, Jul 16, 2015 at 09:26:21AM +0200, Igor Mammedov wrote: > On Wed, 15 Jul 2015 19:32:31 +0300 > "Michael S. Tsirkin" wrote: > > > On Wed, Jul 15, 2015 at 05:12:01PM +0200, Igor Mammedov wrote: > > > On Thu, 9 Jul 2015 13:47:17 +0200 > > > Igor Mammedov wrote: > > > > > > there also is yet another issue with vhost-user. It also has > > > very low limit on amount of memory regions (if I recall correctly 8) > > > and it's possible to trigger even without memory hotplug. > > > one just need to start QEMU with a several -numa memdev= options > > > to create a necessary amount of memory regions to trigger it. > > > > > > lowrisk option to fix it would be increasing limit in vhost-user > > > backend. > > > > > > another option is disabling vhost and fall-back to virtio, > > > but I don't know much about vhost if it's possible to > > > to switch it off without loosing packets guest was sending > > > at the moment and if it will work at all with vhost. > > > > With vhost-user you can't fall back to virtio: it's > > not an accelerator, it's the backend. > > > > Updating the protocol to support a bigger table > > is possible but old remotes won't be able to support it. > > > it looks like increasing limit is the only option left. > > it's not ideal that old remotes /with hardcoded limit/ > might not be able to handle bigger table but at least > new ones and ones that handle VhostUserMsg payload > dynamically would be able to work without crashing. I think we need a way for hotplug to fail gracefully. As long as we don't implement the hva trick, it's needed for old kernels with vhost in kernel, too. -- MST