[RFC v3 3/3] vhost: Allocate memory for packed vring

[Sahil Siddiq <icegambit91@gmail.com>]

Allocate memory for the packed vq format and support
packed vq in the SVQ "start" and "stop" operations.

Signed-off-by: Sahil Siddiq <sahilcdq@proton.me>
---
Changes v2 -> v3:
* vhost-shadow-virtqueue.c
  (vhost_svq_memory_packed): New function
  (vhost_svq_start):
  - Remove common variables out of if-else branch.
  (vhost_svq_stop):
  - Add support for packed vq.
  (vhost_svq_get_vring_addr): Revert changes
  (vhost_svq_get_vring_addr_packed): Likwise.
* vhost-shadow-virtqueue.h
  - Revert changes made to "vhost_svq_get_vring_addr*"
    functions.
* vhost-vdpa.c: Revert changes.

 hw/virtio/vhost-shadow-virtqueue.c | 56 +++++++++++++++++++++++-------
 hw/virtio/vhost-shadow-virtqueue.h |  4 +++
 2 files changed, 47 insertions(+), 13 deletions(-)

diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
index 4c308ee53d..f4285db2b4 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -645,6 +645,8 @@ void vhost_svq_set_svq_call_fd(VhostShadowVirtqueue *svq, int call_fd)
 
 /**
  * Get the shadow vq vring address.
+ * This is used irrespective of whether the
+ * split or packed vq format is used.
  * @svq: Shadow virtqueue
  * @addr: Destination to store address
  */
@@ -672,6 +674,16 @@ size_t vhost_svq_device_area_size(const VhostShadowVirtqueue *svq)
     return ROUND_UP(used_size, qemu_real_host_page_size());
 }
 
+size_t vhost_svq_memory_packed(const VhostShadowVirtqueue *svq)
+{
+    size_t desc_size = sizeof(struct vring_packed_desc) * svq->num_free;
+    size_t driver_event_suppression = sizeof(struct vring_packed_desc_event);
+    size_t device_event_suppression = sizeof(struct vring_packed_desc_event);
+
+    return ROUND_UP(desc_size + driver_event_suppression + device_event_suppression,
+                    qemu_real_host_page_size());
+}
+
 /**
  * Set a new file descriptor for the guest to kick the SVQ and notify for avail
  *
@@ -726,17 +738,30 @@ void vhost_svq_start(VhostShadowVirtqueue *svq, VirtIODevice *vdev,
 
     svq->vring.num = virtio_queue_get_num(vdev, virtio_get_queue_index(vq));
     svq->num_free = svq->vring.num;
-    svq->vring.desc = mmap(NULL, vhost_svq_driver_area_size(svq),
-                           PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS,
-                           -1, 0);
-    desc_size = sizeof(vring_desc_t) * svq->vring.num;
-    svq->vring.avail = (void *)((char *)svq->vring.desc + desc_size);
-    svq->vring.used = mmap(NULL, vhost_svq_device_area_size(svq),
-                           PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS,
-                           -1, 0);
-    svq->desc_state = g_new0(SVQDescState, svq->vring.num);
-    svq->desc_next = g_new0(uint16_t, svq->vring.num);
-    for (unsigned i = 0; i < svq->vring.num - 1; i++) {
+    svq->is_packed = virtio_vdev_has_feature(svq->vdev, VIRTIO_F_RING_PACKED);
+
+    if (virtio_vdev_has_feature(svq->vdev, VIRTIO_F_RING_PACKED)) {
+        svq->vring_packed.vring.desc = mmap(NULL, vhost_svq_memory_packed(svq),
+                                            PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS,
+                                            -1, 0);
+        desc_size = sizeof(struct vring_packed_desc) * svq->vring.num;
+        svq->vring_packed.vring.driver = (void *)((char *)svq->vring_packed.vring.desc + desc_size);
+        svq->vring_packed.vring.device = (void *)((char *)svq->vring_packed.vring.driver +
+                                                  sizeof(struct vring_packed_desc_event));
+    } else {
+        svq->vring.desc = mmap(NULL, vhost_svq_driver_area_size(svq),
+                               PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS,
+                               -1, 0);
+        desc_size = sizeof(vring_desc_t) * svq->vring.num;
+        svq->vring.avail = (void *)((char *)svq->vring.desc + desc_size);
+        svq->vring.used = mmap(NULL, vhost_svq_device_area_size(svq),
+                               PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS,
+                               -1, 0);
+    }
+
+    svq->desc_state = g_new0(SVQDescState, svq->num_free);
+    svq->desc_next = g_new0(uint16_t, svq->num_free);
+    for (unsigned i = 0; i < svq->num_free - 1; i++) {
         svq->desc_next[i] = cpu_to_le16(i + 1);
     }
 }
@@ -776,8 +801,13 @@ void vhost_svq_stop(VhostShadowVirtqueue *svq)
     svq->vq = NULL;
     g_free(svq->desc_next);
     g_free(svq->desc_state);
-    munmap(svq->vring.desc, vhost_svq_driver_area_size(svq));
-    munmap(svq->vring.used, vhost_svq_device_area_size(svq));
+
+    if (svq->is_packed) {
+        munmap(svq->vring_packed.vring.desc, vhost_svq_memory_packed(svq));
+    } else {
+        munmap(svq->vring.desc, vhost_svq_driver_area_size(svq));
+        munmap(svq->vring.used, vhost_svq_device_area_size(svq));
+    }
     event_notifier_set_handler(&svq->hdev_call, NULL);
 }
 
diff --git a/hw/virtio/vhost-shadow-virtqueue.h b/hw/virtio/vhost-shadow-virtqueue.h
index ee1a87f523..03b722a186 100644
--- a/hw/virtio/vhost-shadow-virtqueue.h
+++ b/hw/virtio/vhost-shadow-virtqueue.h
@@ -67,6 +67,9 @@ struct vring_packed {
 
 /* Shadow virtqueue to relay notifications */
 typedef struct VhostShadowVirtqueue {
+    /* True if packed virtqueue */
+    bool is_packed;
+
     /* Virtio queue shadowing */
     VirtQueue *vq;
 
@@ -150,6 +153,7 @@ void vhost_svq_get_vring_addr(const VhostShadowVirtqueue *svq,
                               struct vhost_vring_addr *addr);
 size_t vhost_svq_driver_area_size(const VhostShadowVirtqueue *svq);
 size_t vhost_svq_device_area_size(const VhostShadowVirtqueue *svq);
+size_t vhost_svq_memory_packed(const VhostShadowVirtqueue *svq);
 
 void vhost_svq_start(VhostShadowVirtqueue *svq, VirtIODevice *vdev,
                      VirtQueue *vq, VhostIOVATree *iova_tree);
-- 
2.45.2