From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:44362) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XYdYL-0001Zu-8D for qemu-devel@nongnu.org; Mon, 29 Sep 2014 12:12:03 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XYdYE-0004cx-5B for qemu-devel@nongnu.org; Mon, 29 Sep 2014 12:11:57 -0400 Received: from mx1.redhat.com ([209.132.183.28]:13122) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XYdYD-0004c8-Ti for qemu-devel@nongnu.org; Mon, 29 Sep 2014 12:11:50 -0400 Date: Mon, 29 Sep 2014 19:15:05 +0300 From: "Michael S. Tsirkin" Message-ID: <20140929161505.GC21268@redhat.com> References: <1411066387-30889-1-git-send-email-mst@redhat.com> <1411066387-30889-15-git-send-email-mst@redhat.com> <20140922192857.18930639@bahia.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140922192857.18930639@bahia.local> Subject: Re: [Qemu-devel] [PULL v3 14/15] virtio-pci: fix migration for pci bus master List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Greg Kurz Cc: Peter Maydell , Jason Wang , qemu-devel@nongnu.org, Anthony Liguori , Alexander Graf On Mon, Sep 22, 2014 at 07:28:57PM +0200, Greg Kurz wrote: > On Thu, 18 Sep 2014 21:54:58 +0300 > "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 VIRTIO_PCI_FLAG_BUS_MASTER_BUG and implement a simpler > > work-around: treat clearing of PCI_COMMAND as a virtio reset. Old > > guests never touch this bit so they will work. > > > > As reset clears device status, DRIVER and MASTER bits are > > now in sync, so we can fix up cross-version migration simply > > by synchronising them, without need to detect a buggy guest > > explicitly. > > > > Drop tracking VIRTIO_PCI_FLAG_BUS_MASTER_BUG completely. > > > > As reset makes the device quiescent, in the future we'll be able to drop > > checking OK bit in a bunch of places. > > > > Cc: Jason Wang > > Cc: Greg Kurz > > Signed-off-by: Michael S. Tsirkin > > --- > > Hi, > > This commit prevents pseries to boot. OK I'll revert for now. > SLOF complains with the following messages: > > Trying to load: from: /pci@800000020000000/scsi@0 ... virtioblk_read failed! status = 255 > virtioblk_read failed! status = 255 > virtioblk_read failed! status = 255 > ... > > I'll try to debug some more. > > Cheers. > > -- > Greg > > > hw/virtio/virtio-pci.c | 39 ++++++++++++++++++++------------------- > > 1 file changed, 20 insertions(+), 19 deletions(-) > > > > diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c > > index a827cd4..f560814 100644 > > --- a/hw/virtio/virtio-pci.c > > +++ b/hw/virtio/virtio-pci.c > > @@ -86,9 +86,6 @@ > > * 12 is historical, and due to x86 page size. */ > > #define VIRTIO_PCI_QUEUE_ADDR_SHIFT 12 > > > > -/* Flags track per-device state like workarounds for quirks in older guests. */ > > -#define VIRTIO_PCI_FLAG_BUS_MASTER_BUG (1 << 0) > > - > > static void virtio_pci_bus_new(VirtioBusState *bus, size_t bus_size, > > VirtIOPCIProxy *dev); > > > > @@ -323,14 +320,6 @@ static void virtio_ioport_write(void *opaque, uint32_t addr, uint32_t val) > > 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. */ > > - if ((val & VIRTIO_CONFIG_S_DRIVER_OK) && > > - !(proxy->pci_dev.config[PCI_COMMAND] & PCI_COMMAND_MASTER)) { > > - proxy->flags |= VIRTIO_PCI_FLAG_BUS_MASTER_BUG; > > - } > > break; > > case VIRTIO_MSI_CONFIG_VECTOR: > > msix_vector_unuse(&proxy->pci_dev, vdev->config_vector); > > @@ -480,13 +469,18 @@ static void virtio_write_config(PCIDevice *pci_dev, uint32_t address, > > VirtIOPCIProxy *proxy = DO_UPCAST(VirtIOPCIProxy, pci_dev, pci_dev); > > VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus); > > > > + uint8_t cmd = proxy->pci_dev.config[PCI_COMMAND]; > > + > > pci_default_write_config(pci_dev, address, val, len); > > > > if (range_covers_byte(address, len, PCI_COMMAND) && > > !(pci_dev->config[PCI_COMMAND] & PCI_COMMAND_MASTER) && > > - !(proxy->flags & VIRTIO_PCI_FLAG_BUS_MASTER_BUG)) { > > + (cmd & PCI_COMMAND_MASTER)) { > > + /* Bus driver disables bus mastering - make it act > > + * as a kind of reset to render the device quiescent. */ > > virtio_pci_stop_ioeventfd(proxy); > > - virtio_set_status(vdev, vdev->status & ~VIRTIO_CONFIG_S_DRIVER_OK); > > + virtio_reset(vdev); > > + msix_unuse_all_vectors(&proxy->pci_dev); > > } > > } > > > > @@ -895,11 +889,19 @@ static void virtio_pci_vmstate_change(DeviceState *d, bool running) > > VirtIODevice *vdev = virtio_bus_get_device(&proxy->bus); > > > > if (running) { > > - /* Try to find out if the guest has bus master disabled, but is > > - in ready state. Then we have a buggy guest OS. */ > > - if ((vdev->status & VIRTIO_CONFIG_S_DRIVER_OK) && > > - !(proxy->pci_dev.config[PCI_COMMAND] & PCI_COMMAND_MASTER)) { > > - proxy->flags |= VIRTIO_PCI_FLAG_BUS_MASTER_BUG; > > + /* 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. > > + Note: this only makes a difference when migrating > > + across QEMU versions from an old QEMU, as for new QEMU > > + bus master and driver bits are always in sync. > > + TODO: consider enabling conditionally for compat machine types. */ > > + if (vdev->status & (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); > > } > > virtio_pci_start_ioeventfd(proxy); > > } else { > > @@ -1040,7 +1042,6 @@ static void virtio_pci_reset(DeviceState *qdev) > > virtio_pci_stop_ioeventfd(proxy); > > virtio_bus_reset(bus); > > msix_unuse_all_vectors(&proxy->pci_dev); > > - proxy->flags &= ~VIRTIO_PCI_FLAG_BUS_MASTER_BUG; > > } > > > > static Property virtio_pci_properties[] = {