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" <m...@redhat.com> 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 <jasow...@redhat.com>
> > Cc: Greg Kurz <gk...@linux.vnet.ibm.com>
> > Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
> > ---
>
> Hi,
>
> This commit prevents pseries to boot. 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.
A trace recording all reads and writes of pci status
and virtio status would help.
Thanks!
> --
> 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[] = {
