Re: [PATCH v4 4/4] virtio: Convert feature properties to OnOffAuto

[Lei Yang]

I tested this series of patches v4 with virtio-net regression tests,
everything works fine. And the qemu core dump issues that hit it on v3
have gone.

Tested-by: Lei Yang <leiyang@redhat.com>

On Wed, Jan 8, 2025 at 2:18 PM Akihiko Odaki <akihiko.odaki@daynix.com> wrote:
>
> Some features are not always available with vhost. Legacy features are
> not available with vp_vdpa in particular. virtio devices used to disable
> them when not available even if the corresponding properties were
> explicitly set to "on".
>
> QEMU already has OnOffAuto type, which includes the "auto" value to let
> it automatically decide the effective value. Convert feature properties
> to OnOffAuto and set them "auto" by default to utilize it. This allows
> QEMU to report an error if they are set "on" and the corresponding
> features are not available.
>
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> ---
>  include/hw/virtio/virtio.h | 38 +++++++++++++++++++++-----------------
>  hw/core/machine.c          |  4 +++-
>  hw/virtio/virtio-bus.c     | 14 ++++++++++++--
>  hw/virtio/virtio.c         |  4 +++-
>  4 files changed, 39 insertions(+), 21 deletions(-)
>
> diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
> index 638691028050..b854c2cb1d04 100644
> --- a/include/hw/virtio/virtio.h
> +++ b/include/hw/virtio/virtio.h
> @@ -113,7 +113,8 @@ struct VirtIODevice
>      uint16_t queue_sel;
>      /**
>       * These fields represent a set of VirtIO features at various
> -     * levels of the stack. @host_features indicates the complete
> +     * levels of the stack. @requested_features indicates the feature
> +     * set the user requested. @host_features indicates the complete
>       * feature set the VirtIO device can offer to the driver.
>       * @guest_features indicates which features the VirtIO driver has
>       * selected by writing to the feature register. Finally
> @@ -121,6 +122,7 @@ struct VirtIODevice
>       * backend (e.g. vhost) and could potentially be a subset of the
>       * total feature set offered by QEMU.
>       */
> +    OnOffAutoBit64 requested_features;
>      uint64_t host_features;
>      uint64_t guest_features;
>      uint64_t backend_features;
> @@ -149,6 +151,7 @@ struct VirtIODevice
>      bool started;
>      bool start_on_kick; /* when virtio 1.0 feature has not been negotiated */
>      bool disable_legacy_check;
> +    bool force_features_auto;
>      bool vhost_started;
>      VMChangeStateEntry *vmstate;
>      char *bus_name;
> @@ -376,22 +379,23 @@ typedef struct VirtIOSCSIConf VirtIOSCSIConf;
>  typedef struct VirtIORNGConf VirtIORNGConf;
>
>  #define DEFINE_VIRTIO_COMMON_FEATURES(_state, _field) \
> -    DEFINE_PROP_BIT64("indirect_desc", _state, _field,    \
> -                      VIRTIO_RING_F_INDIRECT_DESC, true), \
> -    DEFINE_PROP_BIT64("event_idx", _state, _field,        \
> -                      VIRTIO_RING_F_EVENT_IDX, true),     \
> -    DEFINE_PROP_BIT64("notify_on_empty", _state, _field,  \
> -                      VIRTIO_F_NOTIFY_ON_EMPTY, true), \
> -    DEFINE_PROP_BIT64("any_layout", _state, _field, \
> -                      VIRTIO_F_ANY_LAYOUT, true), \
> -    DEFINE_PROP_BIT64("iommu_platform", _state, _field, \
> -                      VIRTIO_F_IOMMU_PLATFORM, false), \
> -    DEFINE_PROP_BIT64("packed", _state, _field, \
> -                      VIRTIO_F_RING_PACKED, false), \
> -    DEFINE_PROP_BIT64("queue_reset", _state, _field, \
> -                      VIRTIO_F_RING_RESET, true), \
> -    DEFINE_PROP_BIT64("in_order", _state, _field, \
> -                      VIRTIO_F_IN_ORDER, false)
> +    DEFINE_PROP_ON_OFF_AUTO_BIT64("indirect_desc", _state, _field, \
> +                                  VIRTIO_RING_F_INDIRECT_DESC, \
> +                                  ON_OFF_AUTO_AUTO), \
> +    DEFINE_PROP_ON_OFF_AUTO_BIT64("event_idx", _state, _field, \
> +                                  VIRTIO_RING_F_EVENT_IDX, 
> ON_OFF_AUTO_AUTO), \
> +    DEFINE_PROP_ON_OFF_AUTO_BIT64("notify_on_empty", _state, _field, \
> +                                  VIRTIO_F_NOTIFY_ON_EMPTY, 
> ON_OFF_AUTO_AUTO), \
> +    DEFINE_PROP_ON_OFF_AUTO_BIT64("any_layout", _state, _field, \
> +                                  VIRTIO_F_ANY_LAYOUT, ON_OFF_AUTO_AUTO), \
> +    DEFINE_PROP_ON_OFF_AUTO_BIT64("iommu_platform", _state, _field, \
> +                                  VIRTIO_F_IOMMU_PLATFORM, ON_OFF_AUTO_OFF), 
> \
> +    DEFINE_PROP_ON_OFF_AUTO_BIT64("packed", _state, _field, \
> +                                  VIRTIO_F_RING_PACKED, ON_OFF_AUTO_OFF), \
> +    DEFINE_PROP_ON_OFF_AUTO_BIT64("queue_reset", _state, _field, \
> +                                  VIRTIO_F_RING_RESET, ON_OFF_AUTO_AUTO), \
> +    DEFINE_PROP_ON_OFF_AUTO_BIT64("in_order", _state, _field, \
> +                                  VIRTIO_F_IN_ORDER, ON_OFF_AUTO_OFF)
>
>  hwaddr virtio_queue_get_desc_addr(VirtIODevice *vdev, int n);
>  bool virtio_queue_enabled_legacy(VirtIODevice *vdev, int n);
> diff --git a/hw/core/machine.c b/hw/core/machine.c
> index c949af97668d..bff26b95dd74 100644
> --- a/hw/core/machine.c
> +++ b/hw/core/machine.c
> @@ -36,7 +36,9 @@
>  #include "hw/virtio/virtio-iommu.h"
>  #include "audio/audio.h"
>
> -GlobalProperty hw_compat_9_2[] = {};
> +GlobalProperty hw_compat_9_2[] = {
> +    { TYPE_VIRTIO_DEVICE, "x-force-features-auto", "on" },
> +};
>  const size_t hw_compat_9_2_len = G_N_ELEMENTS(hw_compat_9_2);
>
>  GlobalProperty hw_compat_9_1[] = {
> diff --git a/hw/virtio/virtio-bus.c b/hw/virtio/virtio-bus.c
> index 896feb37a1ca..75d433b252d5 100644
> --- a/hw/virtio/virtio-bus.c
> +++ b/hw/virtio/virtio-bus.c
> @@ -50,6 +50,7 @@ void virtio_bus_device_plugged(VirtIODevice *vdev, Error 
> **errp)
>      bool has_iommu = virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM);
>      bool vdev_has_iommu;
>      Error *local_err = NULL;
> +    uint64_t features;
>
>      DPRINTF("%s: plug device.\n", qbus->name);
>
> @@ -63,13 +64,22 @@ void virtio_bus_device_plugged(VirtIODevice *vdev, Error 
> **errp)
>
>      /* Get the features of the plugged device. */
>      assert(vdc->get_features != NULL);
> -    vdev->host_features = vdc->get_features(vdev, vdev->host_features,
> -                                            &local_err);
> +    features = vdev->host_features | vdev->requested_features.auto_bits |
> +               vdev->requested_features.on_bits;
> +    features = vdc->get_features(vdev, features, &local_err);
>      if (local_err) {
>          error_propagate(errp, local_err);
>          return;
>      }
>
> +    if (!vdev->force_features_auto &&
> +        (features & vdev->requested_features.on_bits) != 
> vdev->requested_features.on_bits) {
> +        error_setg(errp, "A requested feature is not supported by the 
> device");
> +        return;
> +    }
> +
> +    vdev->host_features = features;
> +
>      if (klass->device_plugged != NULL) {
>          klass->device_plugged(qbus->parent, &local_err);
>      }
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 85110bce3744..83f803fc703d 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -4013,11 +4013,13 @@ static void virtio_device_instance_finalize(Object 
> *obj)
>  }
>
>  static const Property virtio_properties[] = {
> -    DEFINE_VIRTIO_COMMON_FEATURES(VirtIODevice, host_features),
> +    DEFINE_VIRTIO_COMMON_FEATURES(VirtIODevice, requested_features),
>      DEFINE_PROP_BOOL("use-started", VirtIODevice, use_started, true),
>      DEFINE_PROP_BOOL("use-disabled-flag", VirtIODevice, use_disabled_flag, 
> true),
>      DEFINE_PROP_BOOL("x-disable-legacy-check", VirtIODevice,
>                       disable_legacy_check, false),
> +    DEFINE_PROP_BOOL("x-force-features-auto", VirtIODevice,
> +                     force_features_auto, false),
>  };
>
>  static int virtio_device_start_ioeventfd_impl(VirtIODevice *vdev)
>
> --
> 2.47.1
>