From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33084) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XgXjC-0007v8-Bg for qemu-devel@nongnu.org; Tue, 21 Oct 2014 07:35:58 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XgXj4-0005zy-My for qemu-devel@nongnu.org; Tue, 21 Oct 2014 07:35:50 -0400 Message-ID: <5446450B.8000600@suse.de> Date: Tue, 21 Oct 2014 13:35:39 +0200 From: Alexander Graf MIME-Version: 1.0 References: <1413788223-16235-1-git-send-email-mst@redhat.com> <54453398.2060102@suse.de> <20141021101650.GA22793@redhat.com> In-Reply-To: <20141021101650.GA22793@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v3] virtio-pci: fix migration for pci bus master List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: qemu-ppc@nongnu.org, qemu-devel@nongnu.org, Anthony Liguori On 21.10.14 12:16, Michael S. Tsirkin wrote: > On Mon, Oct 20, 2014 at 06:08:56PM +0200, Alexander Graf wrote: >> >> >> On 20.10.14 08:58, Michael S. Tsirkin wrote: >>> Current support for bus master (clearing OK bit) together with the need to >>> support guests which do not enable PCI bus mastering, leads to extra state in >>> VIRTIO_PCI_FLAG_BUS_MASTER_BUG bit, which isn't robust in case of cross-version >>> migration for the case when guests use the device before setting DRIVER_OK. >>> >>> Rip out this code, and replace it: >>> - Modern QEMU doesn't need VIRTIO_PCI_FLAG_BUS_MASTER_BUG >>> so just drop it for latest machine type. >>> - For compat machine types, set PCI_COMMAND if DRIVER_OK >>> is set. >>> >>> As this is needed for 2.1 for both pc and ppc, move PC_COMPAT macros from pc.h >>> to a new common header. >>> >>> Reviewed-by: Greg Kurz >>> Tested-by: Greg Kurz >>> Signed-off-by: Michael S. Tsirkin >>> --- >>> >>> Alexander, could you pls ack me merging this? >>> Thanks! >> >> Have you tried whether this works with old kernel versions? We >> introduced the broken flag for very specific old kernel versions that >> got their flags wrong IIRC. >> >> >> Alex > > Yes. The point is that since 2.1 the broken flag isn't effective > anymore: when bus master is off, PCI blocks outgoing transactions and > setting internal flags isn't going to help. > > Instead, we detect a buggy guest and immediately enable bus master for > it - no need for a separate flag. Ok, works for me then. Alex