[PATCH RFC v2 07/13] vhost: add support for negotiating extended features

[Paolo Abeni <pabeni@redhat.com>]

Similar to virtio infra, vhost core maintain the features status
in the full extended format and allow the devices to implement
extended version of the getter/setter.

Note that 'protocol_features' are not extended: they are only
used by vhost-user, and the latter device is not going to implement
extended features soon.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
v1 -> v2:
  - uint128_t -> uint64_t[]
  - add _ex() variant of features manipulation helpers
---
 hw/virtio/vhost.c                 | 73 +++++++++++++++++++++++++++----
 include/hw/virtio/vhost-backend.h |  6 +++
 include/hw/virtio/vhost.h         | 36 +++++++++++++--
 3 files changed, 102 insertions(+), 13 deletions(-)

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index fc43853704..2eee9b0886 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -985,20 +985,34 @@ static int vhost_virtqueue_set_addr(struct vhost_dev *dev,
 static int vhost_dev_set_features(struct vhost_dev *dev,
                                   bool enable_log)
 {
-    uint64_t features = dev->acked_features;
+    uint64_t features[VIRTIO_FEATURES_DWORDS];
     int r;
+
+    virtio_features_copy(features, dev->acked_features_array);
     if (enable_log) {
-        features |= 0x1ULL << VHOST_F_LOG_ALL;
+        virtio_add_feature_ex(features, VHOST_F_LOG_ALL);
     }
     if (!vhost_dev_has_iommu(dev)) {
-        features &= ~(0x1ULL << VIRTIO_F_IOMMU_PLATFORM);
+        virtio_clear_feature_ex(features, VIRTIO_F_IOMMU_PLATFORM);
     }
     if (dev->vhost_ops->vhost_force_iommu) {
         if (dev->vhost_ops->vhost_force_iommu(dev) == true) {
-            features |= 0x1ULL << VIRTIO_F_IOMMU_PLATFORM;
+            virtio_add_feature_ex(features, VIRTIO_F_IOMMU_PLATFORM);
        }
     }
-    r = dev->vhost_ops->vhost_set_features(dev, features);
+
+    if (virtio_features_use_extended(features) &&
+        !dev->vhost_ops->vhost_set_features_ex) {
+        VHOST_OPS_DEBUG(r, "extended features without device support");
+        r = -EINVAL;
+        goto out;
+    }
+
+    if (dev->vhost_ops->vhost_set_features_ex) {
+        r = dev->vhost_ops->vhost_set_features_ex(dev, features);
+    } else {
+        r = dev->vhost_ops->vhost_set_features(dev, features[0]);
+    }
     if (r < 0) {
         VHOST_OPS_DEBUG(r, "vhost_set_features failed");
         goto out;
@@ -1506,12 +1520,27 @@ static void vhost_virtqueue_cleanup(struct vhost_virtqueue *vq)
     }
 }
 
+static int vhost_dev_get_features(struct vhost_dev *hdev,
+                                  uint64_t *features)
+{
+    uint64_t features64;
+    int r;
+
+    if (hdev->vhost_ops->vhost_get_features_ex) {
+        return hdev->vhost_ops->vhost_get_features_ex(hdev, features);
+    }
+
+    r = hdev->vhost_ops->vhost_get_features(hdev, &features64);
+    virtio_features_from_u64(features, features64);
+    return r;
+}
+
 int vhost_dev_init(struct vhost_dev *hdev, void *opaque,
                    VhostBackendType backend_type, uint32_t busyloop_timeout,
                    Error **errp)
 {
+    uint64_t features[VIRTIO_FEATURES_DWORDS];
     unsigned int used, reserved, limit;
-    uint64_t features;
     int i, r, n_initialized_vqs = 0;
 
     hdev->vdev = NULL;
@@ -1531,7 +1560,7 @@ int vhost_dev_init(struct vhost_dev *hdev, void *opaque,
         goto fail;
     }
 
-    r = hdev->vhost_ops->vhost_get_features(hdev, &features);
+    r = vhost_dev_get_features(hdev, features);
     if (r < 0) {
         error_setg_errno(errp, -r, "vhost_get_features failed");
         goto fail;
@@ -1569,7 +1598,7 @@ int vhost_dev_init(struct vhost_dev *hdev, void *opaque,
         }
     }
 
-    hdev->features = features;
+    virtio_features_copy(hdev->features_array, features);
 
     hdev->memory_listener = (MemoryListener) {
         .name = "vhost",
@@ -1592,7 +1621,7 @@ int vhost_dev_init(struct vhost_dev *hdev, void *opaque,
     };
 
     if (hdev->migration_blocker == NULL) {
-        if (!(hdev->features & (0x1ULL << VHOST_F_LOG_ALL))) {
+        if (!virtio_has_feature_ex(hdev->features_array, VHOST_F_LOG_ALL)) {
             error_setg(&hdev->migration_blocker,
                        "Migration disabled: vhost lacks VHOST_F_LOG_ALL feature.");
         } else if (vhost_dev_log_is_shared(hdev) && !qemu_memfd_alloc_check()) {
@@ -1875,6 +1904,20 @@ uint64_t vhost_get_features(struct vhost_dev *hdev, const int *feature_bits,
     return features;
 }
 
+void vhost_get_features_ex(struct vhost_dev *hdev,
+                           const int *feature_bits,
+                           uint64_t *features)
+{
+    const int *bit = feature_bits;
+
+    while (*bit != VHOST_INVALID_FEATURE_BIT) {
+        if (!virtio_has_feature_ex(hdev->features_array, *bit)) {
+            virtio_clear_feature_ex(features, *bit);
+        }
+        bit++;
+    }
+}
+
 void vhost_ack_features(struct vhost_dev *hdev, const int *feature_bits,
                         uint64_t features)
 {
@@ -1888,6 +1931,18 @@ void vhost_ack_features(struct vhost_dev *hdev, const int *feature_bits,
     }
 }
 
+void vhost_ack_features_ex(struct vhost_dev *hdev, const int *feature_bits,
+                           const uint64_t *features)
+{
+    const int *bit = feature_bits;
+    while (*bit != VHOST_INVALID_FEATURE_BIT) {
+        if (virtio_has_feature_ex(features, *bit)) {
+            virtio_add_feature_ex(hdev->acked_features_array, *bit);
+        }
+        bit++;
+    }
+}
+
 int vhost_dev_get_config(struct vhost_dev *hdev, uint8_t *config,
                          uint32_t config_len, Error **errp)
 {
diff --git a/include/hw/virtio/vhost-backend.h b/include/hw/virtio/vhost-backend.h
index d6df209a2f..ff94fa1734 100644
--- a/include/hw/virtio/vhost-backend.h
+++ b/include/hw/virtio/vhost-backend.h
@@ -95,6 +95,10 @@ typedef int (*vhost_new_worker_op)(struct vhost_dev *dev,
                                    struct vhost_worker_state *worker);
 typedef int (*vhost_free_worker_op)(struct vhost_dev *dev,
                                     struct vhost_worker_state *worker);
+typedef int (*vhost_set_features_ex_op)(struct vhost_dev *dev,
+                                        const uint64_t *features);
+typedef int (*vhost_get_features_ex_op)(struct vhost_dev *dev,
+                                        uint64_t *features);
 typedef int (*vhost_set_features_op)(struct vhost_dev *dev,
                                      uint64_t features);
 typedef int (*vhost_get_features_op)(struct vhost_dev *dev,
@@ -186,6 +190,8 @@ typedef struct VhostOps {
     vhost_free_worker_op vhost_free_worker;
     vhost_get_vring_worker_op vhost_get_vring_worker;
     vhost_attach_vring_worker_op vhost_attach_vring_worker;
+    vhost_set_features_ex_op vhost_set_features_ex;
+    vhost_get_features_ex_op vhost_get_features_ex;
     vhost_set_features_op vhost_set_features;
     vhost_get_features_op vhost_get_features;
     vhost_set_backend_cap_op vhost_set_backend_cap;
diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
index 38800a7156..2eec457559 100644
--- a/include/hw/virtio/vhost.h
+++ b/include/hw/virtio/vhost.h
@@ -106,9 +106,9 @@ struct vhost_dev {
      * future use should be discouraged and the variable retired as
      * its easy to confuse with the VirtIO backend_features.
      */
-    uint64_t features;
-    uint64_t acked_features;
-    uint64_t backend_features;
+    VIRTIO_DECLARE_FEATURES(features);
+    VIRTIO_DECLARE_FEATURES(acked_features);
+    VIRTIO_DECLARE_FEATURES(backend_features);
 
     /**
      * @protocol_features: is the vhost-user only feature set by
@@ -310,9 +310,25 @@ void vhost_virtqueue_mask(struct vhost_dev *hdev, VirtIODevice *vdev, int n,
  * is supported by the vhost backend (hdev->features), the supported
  * feature_bits and the requested feature set.
  */
-uint64_t vhost_get_features(struct vhost_dev *hdev, const int *feature_bits,
+uint64_t vhost_get_features(struct vhost_dev *hdev,
+                            const int *feature_bits,
                             uint64_t features);
 
+/**
+ * vhost_get_features_ex() - sanitize the extended features set
+ * @hdev: common vhost_dev structure
+ * @feature_bits: pointer to terminated table of feature bits
+ * @features: original features set, filtered out on return
+ *
+ * This is the extended variant of vhost_get_features(), supporting the
+ * the extended features set. Filter it with the intersection of what is
+ * supported by the vhost backend (hdev->features) and the supported
+ * feature_bits.
+ */
+void vhost_get_features_ex(struct vhost_dev *hdev,
+                           const int *feature_bits,
+                           uint64_t *features);
+
 /**
  * vhost_ack_features() - set vhost acked_features
  * @hdev: common vhost_dev structure
@@ -324,6 +340,18 @@ uint64_t vhost_get_features(struct vhost_dev *hdev, const int *feature_bits,
  */
 void vhost_ack_features(struct vhost_dev *hdev, const int *feature_bits,
                         uint64_t features);
+
+/**
+ * vhost_ack_features_ex() - set vhost full set of acked_features
+ * @hdev: common vhost_dev structure
+ * @feature_bits: pointer to terminated table of feature bits
+ * @features: requested feature set
+ *
+ * This sets the internal hdev->acked_features to the intersection of
+ * the backends advertised features and the supported feature_bits.
+ */
+void vhost_ack_features_ex(struct vhost_dev *hdev, const int *feature_bits,
+                           const uint64_t *features);
 unsigned int vhost_get_max_memslots(void);
 unsigned int vhost_get_free_memslots(void);
 
-- 
2.50.0