From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43755) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XTTIE-0001jh-P7 for qemu-devel@nongnu.org; Mon, 15 Sep 2014 06:14:04 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XTTI3-0005Ub-44 for qemu-devel@nongnu.org; Mon, 15 Sep 2014 06:13:58 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44644) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XTTI2-0005UN-TZ for qemu-devel@nongnu.org; Mon, 15 Sep 2014 06:13:47 -0400 Date: Mon, 15 Sep 2014 18:13:40 +0800 From: Amos Kong Message-ID: <20140915101340.GB17501@zen.redhat.com> References: <1410459530-29832-1-git-send-email-mst@redhat.com> <5416B5E1.6050000@redhat.com> <20140915095944.GD31236@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140915095944.GD31236@redhat.com> Subject: Re: [Qemu-devel] [PATCH v5] virtio-pci: enable bus master for old guests List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: Jason Wang , qemu-devel@nongnu.org, Anthony Liguori On Mon, Sep 15, 2014 at 12:59:44PM +0300, Michael S. Tsirkin wrote: > On Mon, Sep 15, 2014 at 05:48:17PM +0800, Jason Wang wrote: > > On 09/12/2014 02:20 AM, Michael S. Tsirkin wrote: > > > commit cc943c36faa192cd4b32af8fe5edb31894017d35 > > > pci: Use bus master address space for delivering MSI/MSI-X messages > > > breaks virtio-net for rhel6.[56] x86 guests because they don't > > > enable bus mastering for virtio PCI devices. For the same reason, > > > rhel6.[56] ppc64 guests cannot boot on a virtio-blk disk anymore. > > > > > > Old guests forgot to enable bus mastering, enable it automatically on > > > DRIVER (guests use some devices before DRIVER_OK). > > > > > > Reported-by: Greg Kurz > > > Signed-off-by: Michael S. Tsirkin > > > --- > > > Sorry, v4 was broken - forgot to commit before git format-patch. > > > Here's the correct version. > > > Still not tested - will do next week. > > > Testing reports appreciated meanwhile. > > > > > > hw/virtio/virtio-pci.c | 10 ++++++++++ > > > 1 file changed, 10 insertions(+) > > > > > > diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c > > > index ddb5da1..a827cd4 100644 > > > --- a/hw/virtio/virtio-pci.c > > > +++ b/hw/virtio/virtio-pci.c > > > @@ -314,6 +314,16 @@ static void virtio_ioport_write(void *opaque, uint32_t addr, uint32_t val) > > > msix_unuse_all_vectors(&proxy->pci_dev); > > > } > > > > > > + /* Linux before 2.6.34 drives the device without enabling > > > + the PCI device bus master bit. Enable it automatically > > > + for the guest. This is a PCI spec violation but so is > > > + initiating DMA with bus master bit clear. */ > > > + if (val == (VIRTIO_CONFIG_S_ACKNOWLEDGE | VIRTIO_CONFIG_S_DRIVER)) { > > > + pci_default_write_config(&proxy->pci_dev, PCI_COMMAND, > > > + proxy->pci_dev.config[PCI_COMMAND] | > > > + PCI_COMMAND_MASTER, 1); > > > + } > > > + > > > /* Linux before 2.6.34 sets the device as OK without enabling > > > the PCI device bus master bit. In this case we need to disable > > > some safety checks. */ > > > > So with this patch, we can also remove the detecting and handling of > > VIRTIO_PCI_FLAG_BUS_MATER_BUG? > > Yes - I sent a follow-up patch to do that. I will check if this patch fixed this bug (it seems WIN8r2 doesn't set BUS_MASTER bit correctly): https://bugzilla.redhat.com/show_bug.cgi?id=1090237 -- Amos.