From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=46876 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PStGj-0006Pw-NI for qemu-devel@nongnu.org; Wed, 15 Dec 2010 10:27:54 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PStGi-00054c-CT for qemu-devel@nongnu.org; Wed, 15 Dec 2010 10:27:53 -0500 Received: from mx1.redhat.com ([209.132.183.28]:20709) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PStGi-00054E-2r for qemu-devel@nongnu.org; Wed, 15 Dec 2010 10:27:52 -0500 Subject: Re: [Qemu-devel] Re: [PATCH] PCI: Bus number from the bridge, not the device From: Alex Williamson In-Reply-To: <20101215095618.GB28825@redhat.com> References: <20101004215311.17070.54862.stgit@s20.home> <20101108112227.GA1075@redhat.com> <1292270663.2857.129.camel@x201> <20101214044658.GF9554@redhat.com> <1292302161.2857.144.camel@x201> <20101214045715.GG9554@redhat.com> <1292303064.2857.151.camel@x201> <20101214122630.GB19950@redhat.com> <1292351693.2862.9.camel@x201> <20101215095618.GB28825@redhat.com> Content-Type: text/plain; charset="UTF-8" Date: Wed, 15 Dec 2010 08:27:49 -0700 Message-ID: <1292426869.2862.19.camel@x201> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: yamahata@valinux.co.jp, qemu-devel@nongnu.org On Wed, 2010-12-15 at 11:56 +0200, Michael S. Tsirkin wrote: > On Tue, Dec 14, 2010 at 11:34:53AM -0700, Alex Williamson wrote: > > On Tue, 2010-12-14 at 14:26 +0200, Michael S. Tsirkin wrote: > > > On Mon, Dec 13, 2010 at 10:04:24PM -0700, Alex Williamson wrote: > > > > > > > > I've only ever seen config[PCI_SECONDARY_BUS] be non-zero for an > > > > assigned device, so I'm pretty sure we're not going to hurt migration, > > > > but the code is clearly wrong and I'd like to make sure we don't trip on > > > > a migration failure for a minor device config space change. > > > > > > Which reminds me: maybe just mark nested bridges as non-migrateable > > > for now? Care writing such a patch? > > > > Hmm, this is trickier than it sounds. > > Hmm, since 0 is put in the path instead of the bridge number, > will the correct bridge be restored? > > > We're really only broken wrt > > migration if a device under a bridge calls qemu_ram_alloc. > > I guess there's more broken-ness. What exactly breaks qemu_ram_alloc? You're right, it's more broken than that. Anything that calls get_dev_path is broken for migration of bridges since the path is determined before the guest updates bus numbers. That includes qemu_ram_alloc and vmstate. I was only looking at the qemu_ram_alloc side. So perhaps the right answer, for the moment, is to block migration if there's a p2p bridge. Alex > > Any device > > is free to do this, but typically it only happens via > > pci_add_option_rom() (not counting vga as typical). So maybe the better > > approach for now is to prevent the problem by disallowing option ROMs > > for devices below a bridge. We obviously risk devices coming along that > > allocate RAM on their own, but we could still allow the most common > > issue with almost no lost functionality (assuming no one wants to boot > > off that nested device). Thoughts? Thanks, > > > > Alex