Re: [Qemu-devel] [PATCH] virtio: hide legacy features from modern guests

[Jason Wang <jasowang@redhat.com>]

On 07/22/2015 06:11 PM, Michael S. Tsirkin wrote:
> NOTIFY_ON_EMPTY, ANY_LAYOUT and BAD are only valid on the legacy
> interface.
>
> Hide them from modern guests.
>
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

Should we do the same for device specific legacy feature bits?

> ---
>  include/hw/virtio/virtio.h | 4 ++++
>  hw/virtio/virtio-pci.c     | 3 ++-
>  2 files changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> index fbb3c06..cbe3a5a 100644
> --- a/include/hw/virtio/virtio.h
> +++ b/include/hw/virtio/virtio.h
> @@ -25,6 +25,10 @@
>  /* A guest should never accept this.  It implies negotiation is broken. */
>  #define VIRTIO_F_BAD_FEATURE		30
>  
> +#define VIRTIO_LEGACY_FEATURES ((0x1ULL << VIRTIO_F_BAD_FEATURE) | \
> +                                (0x1ULL << VIRTIO_F_NOTIFY_ON_EMPTY) | \
> +                                (0x1ULL << VIRTIO_F_ANY_LAYOUT))
> +
>  struct VirtQueue;
>  
>  static inline hwaddr vring_align(hwaddr addr,
> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> index 283401a..db8f27c 100644
> --- a/hw/virtio/virtio-pci.c
> +++ b/hw/virtio/virtio-pci.c
> @@ -1095,7 +1095,8 @@ static uint64_t virtio_pci_common_read(void *opaque, hwaddr addr,
>          break;
>      case VIRTIO_PCI_COMMON_DF:
>          if (proxy->dfselect <= 1) {
> -            val = vdev->host_features >> (32 * proxy->dfselect);
> +            val = (vdev->host_features & ~VIRTIO_LEGACY_FEATURES) >>
> +                (32 * proxy->dfselect);
>          }
>          break;
>      case VIRTIO_PCI_COMMON_GFSELECT: