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.
--
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[] = {
