On Wed, Mar 11, 2015 at 07:04:38PM +0100, Greg Kurz wrote:
> vhost is seriously broken with ppc64le guests, even in the supposedly
> supported case where the host is ppc64le and we don't need cross-endian
> support.
>
> The TX virtqueue fails to be handled by vhost and falls back to QEMU.
> Despite this unexpected scenario where RX is vhost and TX is QEMU, the
> guest runs well with reduced upload performances... until you reboot,
> migrate, managed save or in fact any operation that causes vhost_net
> to be re-started. Network connectivity is then permanantly lost for
> the guest.
>
> TX falling back to QEMU is the result of a failed MMIO store emulation
> in KVM. Debugging shows that:
>
> kvmppc_emulate_mmio()
> |
> +-> kvmppc_handle_store()
> |
> +-> kvm_io_bus_write()
> |
> +-> __kvm_io_bus_write() returns -EOPNOTSUPP
>
> This happens because no matching device was found:
>
> __kvm_io_bus_write()
> |
> +->kvm_iodevice_write()
> |
> +->ioeventfd_write()
> |
> +->ioeventfd_in_range() returns false for all registered vrings
>
> Extra debugging shows that the TX vring number (16-bit) is supposed to
> be 0x0100 but QEMU passes 0x0001 to KVM... This happens *again* because
> QEMU still assumes powerpc is big endian (TARGET_WORDS_BIGENDIAN) by
> default.
>
> This patch adds an extra swap in virtio_pci_set_host_notifier_internal()
> to negate the one that is done in adjust_endianness(). Since this is not
> a hot path and we want to keep virtio-pci.o in common-obj, we don't care
> whether the guest is bi-endian or not.
>
> Reported-by: Cédric Le Goater <c...@fr.ibm.com>
> Suggested-by: Michael Roth <mdr...@linux.vnet.ibm.com>
> Signed-off-by: Greg Kurz <gk...@linux.vnet.ibm.com>
I am confused.
The value that notifications use is always LE.
Can't we avoid multiple swaps?
They make my head spin.
> ---
>
> I guess it is also a fix for virtio-1 but I didn't check.
>
> hw/virtio/virtio-pci.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> index e7baf7b..62b04c9 100644
> --- a/hw/virtio/virtio-pci.c
> +++ b/hw/virtio/virtio-pci.c
> @@ -133,6 +133,11 @@ static int virtio_pci_load_queue(DeviceState *d, int n,
> QEMUFile *f)
> return 0;
> }
>
> +static uint16_t cpu_to_host_notifier16(VirtIODevice *vdev, uint16_t val)
> +{
> + return virtio_is_big_endian(vdev) ? val : bswap16(val);
> +}
> +
> static int virtio_pci_set_host_notifier_internal(VirtIOPCIProxy *proxy,
> int n, bool assign, bool
> set_handler)
> {
> @@ -150,10 +155,12 @@ static int
> virtio_pci_set_host_notifier_internal(VirtIOPCIProxy *proxy,
> }
> virtio_queue_set_host_notifier_fd_handler(vq, true, set_handler);
> memory_region_add_eventfd(&proxy->bar, VIRTIO_PCI_QUEUE_NOTIFY, 2,
> - true, n, notifier);
> + true, cpu_to_host_notifier16(vdev, n),
> + notifier);
> } else {
> memory_region_del_eventfd(&proxy->bar, VIRTIO_PCI_QUEUE_NOTIFY, 2,
> - true, n, notifier);
> + true, cpu_to_host_notifier16(vdev, n),
> + notifier);
> virtio_queue_set_host_notifier_fd_handler(vq, false, false);
> event_notifier_cleanup(notifier);
> }
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