[[RFC,v3,07/12] virtio: fill/flush/pop for packed ring

Commit Message

Wei Xu Oct. 11, 2018, 2:08 p.m. UTC

From: Wei Xu <[e-mail]>

Signed-off-by: Wei Xu <[e-mail]>
---
 hw/virtio/virtio.c | 258 ++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 244 insertions(+), 14 deletions(-)

Comments

Jason Wang Oct. 15, 2018, 6:14 a.m. UTC | #1

On 2018年10月11日 22:08, [e-mail] wrote:
> From: Wei Xu <[e-mail]>
>
> Signed-off-by: Wei Xu <[e-mail]>
> ---
>   hw/virtio/virtio.c | 258 ++++++++++++++++++++++++++++++++++++++++++++++++++---
>   1 file changed, 244 insertions(+), 14 deletions(-)
>
> diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
> index 13c6c98..d12a7e3 100644
> --- a/hw/virtio/virtio.c
> +++ b/hw/virtio/virtio.c
> @@ -386,6 +386,21 @@ static void vring_packed_desc_read(VirtIODevice *vdev, VRingPackedDesc *desc,
>       virtio_tswap16s(vdev, &desc->id);
>   }
>   
> +static void vring_packed_desc_write(VirtIODevice *vdev, VRingPackedDesc *desc,
> +                            MemoryRegionCache *cache, int i)
> +{
> +    virtio_tswap64s(vdev, &desc->addr);
> +    virtio_tswap32s(vdev, &desc->len);
> +    virtio_tswap16s(vdev, &desc->id);
> +    virtio_tswap16s(vdev, &desc->flags);
> +    address_space_write_cached(cache,
> +                               sizeof(VRingPackedDesc) * i, desc,
> +                               sizeof(VRingPackedDesc));
> +    address_space_cache_invalidate(cache,
> +                                   sizeof(VRingPackedDesc) * i,
> +                                   sizeof(VRingPackedDesc));
> +}
> +
>   static void vring_packed_desc_read_flags(VirtIODevice *vdev,
>                       VRingPackedDesc *desc, MemoryRegionCache *cache, int i)
>   {
> @@ -559,19 +574,11 @@ bool virtqueue_rewind(VirtQueue *vq, unsigned int num)
>   }
>   
>   /* Called within rcu_read_lock().  */
> -void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
> +static void virtqueue_split_fill(VirtQueue *vq, const VirtQueueElement *elem,
>                       unsigned int len, unsigned int idx)
>   {
>       VRingUsedElem uelem;
>   
> -    trace_virtqueue_fill(vq, elem, len, idx);
> -
> -    virtqueue_unmap_sg(vq, elem, len);
> -
> -    if (unlikely(vq->vdev->broken)) {
> -        return;
> -    }
> -
>       if (unlikely(!vq->vring.used)) {
>           return;
>       }
> @@ -583,16 +590,64 @@ void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
>       vring_used_write(vq, &uelem, idx);
>   }
>   
> -/* Called within rcu_read_lock().  */
> -void virtqueue_flush(VirtQueue *vq, unsigned int count)
> +static void virtqueue_packed_fill(VirtQueue *vq, const VirtQueueElement *elem,
> +                        unsigned int len, unsigned int idx)
>   {
> -    uint16_t old, new;
> +    uint16_t w, head;
> +    VRingMemoryRegionCaches *caches;
> +    VRingPackedDesc desc = {
> +        .addr = 0,
> +        .flags = 0,
> +    };
> +
> +    if (unlikely(!vq->vring.desc)) {
> +        return;
> +    }
> +
> +    caches = vring_get_region_caches(vq);
> +    head = vq->used_idx + idx;
> +    head = head >= vq->vring.num ? (head - vq->vring.num) : head;
> +    vring_packed_desc_read(vq->vdev, &desc, &caches->desc, head);

Is this a must for reading descriptor once more? Shouldn't device 
maintain its own used_wrap_counter?

> +
> +    w = (desc.flags & AVAIL_DESC_PACKED(1)) >> 7;
> +    desc.flags &= ~(AVAIL_DESC_PACKED(1) | USED_DESC_PACKED(1));
> +    desc.flags |= AVAIL_DESC_PACKED(w) | USED_DESC_PACKED(w);
> +    if (!(desc.flags & VRING_DESC_F_INDIRECT)) {
> +        if (!(desc.flags & VRING_DESC_F_WRITE)) {
> +            desc.len = 0;
> +        } else {
> +            desc.len = len;
> +        }
> +    }
> +    vring_packed_desc_write(vq->vdev, &desc, &caches->desc, head);
> +
> +    /* Make sure flags has been updated */
> +    smp_mb();

This is wrong in two places:

- What you want is to make sure flag was updated after all other fields, 
you can do it in vring_packed_desc_write()
- A write barrier instead of a full barrier is needed.

> +}
> +
> +void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
> +                    unsigned int len, unsigned int idx)
> +{
> +    trace_virtqueue_fill(vq, elem, len, idx);
> +
> +    virtqueue_unmap_sg(vq, elem, len);
>   
>       if (unlikely(vq->vdev->broken)) {
> -        vq->inuse -= count;
>           return;
>       }
>   
> +    if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) {
> +        virtqueue_packed_fill(vq, elem, len, idx);
> +    } else {
> +        virtqueue_split_fill(vq, elem, len, idx);
> +    }
> +}
> +
> +/* Called within rcu_read_lock().  */
> +static void virtqueue_split_flush(VirtQueue *vq, unsigned int count)
> +{
> +    uint16_t old, new;
> +
>       if (unlikely(!vq->vring.used)) {
>           return;
>       }
> @@ -608,6 +663,33 @@ void virtqueue_flush(VirtQueue *vq, unsigned int count)
>           vq->signalled_used_valid = false;
>   }
>   
> +static void virtqueue_packed_flush(VirtQueue *vq, unsigned int count)
> +{
> +    if (unlikely(!vq->vring.desc)) {
> +        return;
> +    }
> +
> +    vq->inuse -= count;
> +    vq->used_idx += count;
> +    if (vq->used_idx >= vq->vring.num) {
> +        vq->used_idx -= vq->vring.num;
> +    }
> +}
> +
> +void virtqueue_flush(VirtQueue *vq, unsigned int count)
> +{
> +    if (unlikely(vq->vdev->broken)) {
> +        vq->inuse -= count;
> +        return;
> +    }
> +
> +    if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) {
> +        virtqueue_packed_flush(vq, count);
> +    } else {
> +        virtqueue_split_flush(vq, count);
> +    }
> +}
> +
>   void virtqueue_push(VirtQueue *vq, const VirtQueueElement *elem,
>                       unsigned int len)
>   {
> @@ -1091,7 +1173,7 @@ static void *virtqueue_alloc_element(size_t sz, unsigned out_num, unsigned in_nu
>       return elem;
>   }
>   
> -void *virtqueue_pop(VirtQueue *vq, size_t sz)
> +static void *virtqueue_split_pop(VirtQueue *vq, size_t sz)
>   {
>       unsigned int i, head, max;
>       VRingMemoryRegionCaches *caches;
> @@ -1226,6 +1308,154 @@ err_undo_map:
>       goto done;
>   }
>   
> +static void *virtqueue_packed_pop(VirtQueue *vq, size_t sz)
> +{
> +    unsigned int i, head, max;
> +    VRingMemoryRegionCaches *caches;
> +    MemoryRegionCache indirect_desc_cache = MEMORY_REGION_CACHE_INVALID;
> +    MemoryRegionCache *cache;
> +    int64_t len;
> +    VirtIODevice *vdev = vq->vdev;
> +    VirtQueueElement *elem = NULL;
> +    unsigned out_num, in_num, elem_entries;
> +    hwaddr addr[VIRTQUEUE_MAX_SIZE];
> +    struct iovec iov[VIRTQUEUE_MAX_SIZE];
> +    VRingPackedDesc desc;
> +
> +    if (unlikely(vdev->broken)) {
> +        return NULL;
> +    }
> +
> +    rcu_read_lock();
> +    if (virtio_queue_packed_empty_rcu(vq)) {
> +        goto done;
> +    }
> +
> +    /* When we start there are none of either input nor output. */
> +    out_num = in_num = elem_entries = 0;
> +
> +    max = vq->vring.num;
> +
> +    if (vq->inuse >= vq->vring.num) {
> +        virtio_error(vdev, "Virtqueue size exceeded");
> +        goto done;
> +    }

The above is duplicated with split version, please unify them.

> +
> +    head = vq->last_avail_idx;
> +    i = head;
> +
> +    caches = vring_get_region_caches(vq);
> +    cache = &caches->desc;
> +    vring_packed_desc_read(vdev, &desc, cache, i);
> +    /* Make sure we see all the fields*/
> +    smp_rmb();

This is wrong, as I've pointed out.

> +    if (desc.flags & VRING_DESC_F_INDIRECT) {
> +        if (desc.len % sizeof(VRingPackedDesc)) {
> +            virtio_error(vdev, "Invalid size for indirect buffer table");
> +            goto done;
> +        }
> +
> +        /* loop over the indirect descriptor table */
> +        len = address_space_cache_init(&indirect_desc_cache, vdev->dma_as,
> +                                       desc.addr, desc.len, false);
> +        cache = &indirect_desc_cache;
> +        if (len < desc.len) {
> +            virtio_error(vdev, "Cannot map indirect buffer");
> +            goto done;
> +        }
> +
> +        max = desc.len / sizeof(VRingPackedDesc);
> +        i = 0;
> +        vring_packed_desc_read(vdev, &desc, cache, i);
> +        /* Make sure we see all the fields*/
> +        smp_rmb();
> +    }
> +
> +    /* Collect all the descriptors */
> +    while (1) {
> +        bool map_ok;
> +
> +        if (desc.flags & VRING_DESC_F_WRITE) {
> +            map_ok = virtqueue_map_desc(vdev, &in_num, addr + out_num,
> +                                        iov + out_num,
> +                                        VIRTQUEUE_MAX_SIZE - out_num, true,
> +                                        desc.addr, desc.len);
> +        } else {
> +            if (in_num) {
> +                virtio_error(vdev, "Incorrect order for descriptors");
> +                goto err_undo_map;
> +            }
> +            map_ok = virtqueue_map_desc(vdev, &out_num, addr, iov,
> +                                        VIRTQUEUE_MAX_SIZE, false,
> +                                        desc.addr, desc.len);
> +        }
> +        if (!map_ok) {
> +            goto err_undo_map;
> +        }
> +
> +        /* If we've got too many, that implies a descriptor loop. */
> +        if (++elem_entries > max) {
> +            virtio_error(vdev, "Looped descriptor");
> +            goto err_undo_map;
> +        }
> +
> +        if (++i >= vq->vring.num) {
> +            i -= vq->vring.num;
> +        }
> +
> +        if (desc.flags & VRING_DESC_F_NEXT) {
> +            vring_packed_desc_read(vq->vdev, &desc, cache, i);
> +            /* Make sure we see all the fields*/
> +            smp_rmb();

This looks unnecessary.

Thanks

> +        } else {
> +            break;
> +        }
> +    }
> +
> +    /* Now copy what we have collected and mapped */
> +    elem = virtqueue_alloc_element(sz, out_num, in_num);
> +    for (i = 0; i < out_num; i++) {
> +        elem->out_addr[i] = addr[i];
> +        elem->out_sg[i] = iov[i];
> +    }
> +    for (i = 0; i < in_num; i++) {
> +        elem->in_addr[i] = addr[head + out_num + i];
> +        elem->in_sg[i] = iov[out_num + i];
> +    }
> +
> +    vq->last_avail_idx += (cache == &indirect_desc_cache) ?
> +                          1 : out_num + in_num;
> +    if (vq->last_avail_idx >= vq->vring.num) {
> +        vq->last_avail_idx -= vq->vring.num;
> +        vq->avail_wrap_counter = !vq->avail_wrap_counter;
> +    }
> +    vq->inuse++;
> +
> +    vq->event_idx = vq->last_avail_idx;
> +    vq->event_wrap_counter = vq->avail_wrap_counter;
> +
> +    trace_virtqueue_pop(vq, elem, elem->in_num, elem->out_num);
> +done:
> +    address_space_cache_destroy(&indirect_desc_cache);
> +    rcu_read_unlock();
> +
> +    return elem;
> +
> +err_undo_map:
> +    virtqueue_undo_map_desc(out_num, in_num, iov);
> +    g_free(elem);
> +    goto done;
> +}
> +
> +void *virtqueue_pop(VirtQueue *vq, size_t sz)
> +{
> +    if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) {
> +        return virtqueue_packed_pop(vq, sz);
> +    } else {
> +        return virtqueue_split_pop(vq, sz);
> +    }
> +}
> +
>   /* virtqueue_drop_all:
>    * @vq: The #VirtQueue
>    * Drops all queued buffers and indicates them to the guest

Patch

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 13c6c98..d12a7e3 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -386,6 +386,21 @@  static void vring_packed_desc_read(VirtIODevice *vdev, VRingPackedDesc *desc,
     virtio_tswap16s(vdev, &desc->id);
 }
 
+static void vring_packed_desc_write(VirtIODevice *vdev, VRingPackedDesc *desc,
+                            MemoryRegionCache *cache, int i)
+{
+    virtio_tswap64s(vdev, &desc->addr);
+    virtio_tswap32s(vdev, &desc->len);
+    virtio_tswap16s(vdev, &desc->id);
+    virtio_tswap16s(vdev, &desc->flags);
+    address_space_write_cached(cache,
+                               sizeof(VRingPackedDesc) * i, desc,
+                               sizeof(VRingPackedDesc));
+    address_space_cache_invalidate(cache,
+                                   sizeof(VRingPackedDesc) * i,
+                                   sizeof(VRingPackedDesc));
+}
+
 static void vring_packed_desc_read_flags(VirtIODevice *vdev,
                     VRingPackedDesc *desc, MemoryRegionCache *cache, int i)
 {
@@ -559,19 +574,11 @@  bool virtqueue_rewind(VirtQueue *vq, unsigned int num)
 }
 
 /* Called within rcu_read_lock().  */
-void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
+static void virtqueue_split_fill(VirtQueue *vq, const VirtQueueElement *elem,
                     unsigned int len, unsigned int idx)
 {
     VRingUsedElem uelem;
 
-    trace_virtqueue_fill(vq, elem, len, idx);
-
-    virtqueue_unmap_sg(vq, elem, len);
-
-    if (unlikely(vq->vdev->broken)) {
-        return;
-    }
-
     if (unlikely(!vq->vring.used)) {
         return;
     }
@@ -583,16 +590,64 @@  void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
     vring_used_write(vq, &uelem, idx);
 }
 
-/* Called within rcu_read_lock().  */
-void virtqueue_flush(VirtQueue *vq, unsigned int count)
+static void virtqueue_packed_fill(VirtQueue *vq, const VirtQueueElement *elem,
+                        unsigned int len, unsigned int idx)
 {
-    uint16_t old, new;
+    uint16_t w, head;
+    VRingMemoryRegionCaches *caches;
+    VRingPackedDesc desc = {
+        .addr = 0,
+        .flags = 0,
+    };
+
+    if (unlikely(!vq->vring.desc)) {
+        return;
+    }
+
+    caches = vring_get_region_caches(vq);
+    head = vq->used_idx + idx;
+    head = head >= vq->vring.num ? (head - vq->vring.num) : head;
+    vring_packed_desc_read(vq->vdev, &desc, &caches->desc, head);
+
+    w = (desc.flags & AVAIL_DESC_PACKED(1)) >> 7;
+    desc.flags &= ~(AVAIL_DESC_PACKED(1) | USED_DESC_PACKED(1));
+    desc.flags |= AVAIL_DESC_PACKED(w) | USED_DESC_PACKED(w);
+    if (!(desc.flags & VRING_DESC_F_INDIRECT)) {
+        if (!(desc.flags & VRING_DESC_F_WRITE)) {
+            desc.len = 0;
+        } else {
+            desc.len = len;
+        }
+    }
+    vring_packed_desc_write(vq->vdev, &desc, &caches->desc, head);
+
+    /* Make sure flags has been updated */
+    smp_mb();
+}
+
+void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem,
+                    unsigned int len, unsigned int idx)
+{
+    trace_virtqueue_fill(vq, elem, len, idx);
+
+    virtqueue_unmap_sg(vq, elem, len);
 
     if (unlikely(vq->vdev->broken)) {
-        vq->inuse -= count;
         return;
     }
 
+    if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) {
+        virtqueue_packed_fill(vq, elem, len, idx);
+    } else {
+        virtqueue_split_fill(vq, elem, len, idx);
+    }
+}
+
+/* Called within rcu_read_lock().  */
+static void virtqueue_split_flush(VirtQueue *vq, unsigned int count)
+{
+    uint16_t old, new;
+
     if (unlikely(!vq->vring.used)) {
         return;
     }
@@ -608,6 +663,33 @@  void virtqueue_flush(VirtQueue *vq, unsigned int count)
         vq->signalled_used_valid = false;
 }
 
+static void virtqueue_packed_flush(VirtQueue *vq, unsigned int count)
+{
+    if (unlikely(!vq->vring.desc)) {
+        return;
+    }
+
+    vq->inuse -= count;
+    vq->used_idx += count;
+    if (vq->used_idx >= vq->vring.num) {
+        vq->used_idx -= vq->vring.num;
+    }
+}
+
+void virtqueue_flush(VirtQueue *vq, unsigned int count)
+{
+    if (unlikely(vq->vdev->broken)) {
+        vq->inuse -= count;
+        return;
+    }
+
+    if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) {
+        virtqueue_packed_flush(vq, count);
+    } else {
+        virtqueue_split_flush(vq, count);
+    }
+}
+
 void virtqueue_push(VirtQueue *vq, const VirtQueueElement *elem,
                     unsigned int len)
 {
@@ -1091,7 +1173,7 @@  static void *virtqueue_alloc_element(size_t sz, unsigned out_num, unsigned in_nu
     return elem;
 }
 
-void *virtqueue_pop(VirtQueue *vq, size_t sz)
+static void *virtqueue_split_pop(VirtQueue *vq, size_t sz)
 {
     unsigned int i, head, max;
     VRingMemoryRegionCaches *caches;
@@ -1226,6 +1308,154 @@  err_undo_map:
     goto done;
 }
 
+static void *virtqueue_packed_pop(VirtQueue *vq, size_t sz)
+{
+    unsigned int i, head, max;
+    VRingMemoryRegionCaches *caches;
+    MemoryRegionCache indirect_desc_cache = MEMORY_REGION_CACHE_INVALID;
+    MemoryRegionCache *cache;
+    int64_t len;
+    VirtIODevice *vdev = vq->vdev;
+    VirtQueueElement *elem = NULL;
+    unsigned out_num, in_num, elem_entries;
+    hwaddr addr[VIRTQUEUE_MAX_SIZE];
+    struct iovec iov[VIRTQUEUE_MAX_SIZE];
+    VRingPackedDesc desc;
+
+    if (unlikely(vdev->broken)) {
+        return NULL;
+    }
+
+    rcu_read_lock();
+    if (virtio_queue_packed_empty_rcu(vq)) {
+        goto done;
+    }
+
+    /* When we start there are none of either input nor output. */
+    out_num = in_num = elem_entries = 0;
+
+    max = vq->vring.num;
+
+    if (vq->inuse >= vq->vring.num) {
+        virtio_error(vdev, "Virtqueue size exceeded");
+        goto done;
+    }
+
+    head = vq->last_avail_idx;
+    i = head;
+
+    caches = vring_get_region_caches(vq);
+    cache = &caches->desc;
+    vring_packed_desc_read(vdev, &desc, cache, i);
+    /* Make sure we see all the fields*/
+    smp_rmb();
+    if (desc.flags & VRING_DESC_F_INDIRECT) {
+        if (desc.len % sizeof(VRingPackedDesc)) {
+            virtio_error(vdev, "Invalid size for indirect buffer table");
+            goto done;
+        }
+
+        /* loop over the indirect descriptor table */
+        len = address_space_cache_init(&indirect_desc_cache, vdev->dma_as,
+                                       desc.addr, desc.len, false);
+        cache = &indirect_desc_cache;
+        if (len < desc.len) {
+            virtio_error(vdev, "Cannot map indirect buffer");
+            goto done;
+        }
+
+        max = desc.len / sizeof(VRingPackedDesc);
+        i = 0;
+        vring_packed_desc_read(vdev, &desc, cache, i);
+        /* Make sure we see all the fields*/
+        smp_rmb();
+    }
+
+    /* Collect all the descriptors */
+    while (1) {
+        bool map_ok;
+
+        if (desc.flags & VRING_DESC_F_WRITE) {
+            map_ok = virtqueue_map_desc(vdev, &in_num, addr + out_num,
+                                        iov + out_num,
+                                        VIRTQUEUE_MAX_SIZE - out_num, true,
+                                        desc.addr, desc.len);
+        } else {
+            if (in_num) {
+                virtio_error(vdev, "Incorrect order for descriptors");
+                goto err_undo_map;
+            }
+            map_ok = virtqueue_map_desc(vdev, &out_num, addr, iov,
+                                        VIRTQUEUE_MAX_SIZE, false,
+                                        desc.addr, desc.len);
+        }
+        if (!map_ok) {
+            goto err_undo_map;
+        }
+
+        /* If we've got too many, that implies a descriptor loop. */
+        if (++elem_entries > max) {
+            virtio_error(vdev, "Looped descriptor");
+            goto err_undo_map;
+        }
+
+        if (++i >= vq->vring.num) {
+            i -= vq->vring.num;
+        }
+
+        if (desc.flags & VRING_DESC_F_NEXT) {
+            vring_packed_desc_read(vq->vdev, &desc, cache, i);
+            /* Make sure we see all the fields*/
+            smp_rmb();
+        } else {
+            break;
+        }
+    }
+
+    /* Now copy what we have collected and mapped */
+    elem = virtqueue_alloc_element(sz, out_num, in_num);
+    for (i = 0; i < out_num; i++) {
+        elem->out_addr[i] = addr[i];
+        elem->out_sg[i] = iov[i];
+    }
+    for (i = 0; i < in_num; i++) {
+        elem->in_addr[i] = addr[head + out_num + i];
+        elem->in_sg[i] = iov[out_num + i];
+    }
+
+    vq->last_avail_idx += (cache == &indirect_desc_cache) ?
+                          1 : out_num + in_num;
+    if (vq->last_avail_idx >= vq->vring.num) {
+        vq->last_avail_idx -= vq->vring.num;
+        vq->avail_wrap_counter = !vq->avail_wrap_counter;
+    }
+    vq->inuse++;
+
+    vq->event_idx = vq->last_avail_idx;
+    vq->event_wrap_counter = vq->avail_wrap_counter;
+
+    trace_virtqueue_pop(vq, elem, elem->in_num, elem->out_num);
+done:
+    address_space_cache_destroy(&indirect_desc_cache);
+    rcu_read_unlock();
+
+    return elem;
+
+err_undo_map:
+    virtqueue_undo_map_desc(out_num, in_num, iov);
+    g_free(elem);
+    goto done;
+}
+
+void *virtqueue_pop(VirtQueue *vq, size_t sz)
+{
+    if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) {
+        return virtqueue_packed_pop(vq, sz);
+    } else {
+        return virtqueue_split_pop(vq, sz);
+    }
+}
+
 /* virtqueue_drop_all:
  * @vq: The #VirtQueue
  * Drops all queued buffers and indicates them to the guest