Re: [PATCH v5 4/4] virtio: Convert feature properties to OnOffAuto

Akihiko Odaki Wed, 26 Feb 2025 23:09:33 -0800

On 2025/02/21 0:46, Michael S. Tsirkin wrote:

On Sat, Feb 08, 2025 at 04:51:10PM +0900, Akihiko Odaki 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.od...@daynix.com>

---
  include/hw/virtio/virtio.h | 38 +++++++++++++++++++++-----------------
  hw/core/machine.c          |  1 +
  hw/virtio/virtio-bus.c     | 14 ++++++++++++--
  hw/virtio/virtio.c         |  4 +++-
  4 files changed, 37 insertions(+), 20 deletions(-)

diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index 
638691028050d2599592d8c7e95c75ac3913fbdd..b854c2cb1d04da0a35165289c28f87e8cb869df6
 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 
c23b39949649054ac59d2a9b497f34e1b7bd8d6c..0de04baa61735ff02f797f778c626ef690625ce3
 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -38,6 +38,7 @@

GlobalProperty hw_compat_9_2[] = {

      {"arm-cpu", "backcompat-pauth-default-use-qarma5", "true"},
+    { TYPE_VIRTIO_DEVICE, "x-force-features-auto", "on" },
  };
  const size_t hw_compat_9_2_len = G_N_ELEMENTS(hw_compat_9_2);


Confused why this is on.
If set, this breaks existing setups if they run a configuration vhost
does not support, does it not?
And in particular, aren't some of these features exposed through
libvirt?

This property enforces the existing behavior, which is to disableunsupported features even if they are explicitly set to "on". Itintroduces no breaking change.

diff --git a/hw/virtio/virtio-bus.c b/hw/virtio/virtio-bus.c
index 
896feb37a1caa805543e971c150d3673675b9a6b..75d433b252d5337d91616a2847b3dc12e811c2da
 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 
85110bce37443bb46c4159761af112d0dba466b4..83f803fc703da6257608e21476305c8e9c6a8b07
 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)


--
2.48.1

Re: [PATCH v5 4/4] virtio: Convert feature properties to OnOffAuto

Reply via email to