Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Tiwei Bie <tiwei.bie@intel.com>
To:     mst@redhat.com, virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, netdev@vger.kernel.org
Cc:     jasowang@redhat.com, wexu@redhat.com, jfreimann@redhat.com,
        tiwei.bie@intel.com
Subject: [PATCH RFC 2/2] virtio_ring: support packed ring
Date:   Fri, 23 Feb 2018 19:18:01 +0800
Message-Id: <20180223111801.15240-3-tiwei.bie@intel.com>
In-Reply-To: <20180223111801.15240-1-tiwei.bie@intel.com>
References: <20180223111801.15240-1-tiwei.bie@intel.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
---
 drivers/virtio/virtio_ring.c | 699 +++++++++++++++++++++++++++++++++++++------
 include/linux/virtio_ring.h  |   8 +-
 2 files changed, 618 insertions(+), 89 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index eb30f3e09a47..393778a2f809 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -58,14 +58,14 @@
 
 struct vring_desc_state {
 	void *data;			/* Data for callback. */
-	struct vring_desc *indir_desc;	/* Indirect descriptor, if any. */
+	void *indir_desc;		/* Indirect descriptor, if any. */
+	int num;			/* Descriptor list length. */
 };
 
 struct vring_virtqueue {
 	struct virtqueue vq;
 
-	/* Actual memory layout for this queue */
-	struct vring vring;
+	bool packed;
 
 	/* Can we use weak barriers? */
 	bool weak_barriers;
@@ -87,11 +87,28 @@ struct vring_virtqueue {
 	/* Last used index we've seen. */
 	u16 last_used_idx;
 
-	/* Last written value to avail->flags */
-	u16 avail_flags_shadow;
-
-	/* Last written value to avail->idx in guest byte order */
-	u16 avail_idx_shadow;
+	union {
+		/* Available for split ring */
+		struct {
+			/* Actual memory layout for this queue */
+			struct vring vring;
+
+			/* Last written value to avail->flags */
+			u16 avail_flags_shadow;
+
+			/* Last written value to avail->idx in
+			 * guest byte order */
+			u16 avail_idx_shadow;
+		};
+
+		/* Available for packed ring */
+		struct {
+			/* Actual memory layout for this queue */
+			struct vring_packed vring_packed;
+			u8 wrap_counter : 1;
+			bool chaining;
+		};
+	};
 
 	/* How to notify other side. FIXME: commonalize hcalls! */
 	bool (*notify)(struct virtqueue *vq);
@@ -201,26 +218,37 @@ static dma_addr_t vring_map_single(const struct vring_virtqueue *vq,
 			      cpu_addr, size, direction);
 }
 
-static void vring_unmap_one(const struct vring_virtqueue *vq,
-			    struct vring_desc *desc)
+static void vring_unmap_one(const struct vring_virtqueue *vq, void *_desc)
 {
+	u64 addr;
+	u32 len;
 	u16 flags;
 
 	if (!vring_use_dma_api(vq->vq.vdev))
 		return;
 
-	flags = virtio16_to_cpu(vq->vq.vdev, desc->flags);
+	if (vq->packed) {
+		struct vring_packed_desc *desc = _desc;
+
+		addr = virtio64_to_cpu(vq->vq.vdev, desc->addr);
+		len = virtio32_to_cpu(vq->vq.vdev, desc->len);
+		flags = virtio16_to_cpu(vq->vq.vdev, desc->flags);
+	} else {
+		struct vring_desc *desc = _desc;
+
+		addr = virtio64_to_cpu(vq->vq.vdev, desc->addr);
+		len = virtio32_to_cpu(vq->vq.vdev, desc->len);
+		flags = virtio16_to_cpu(vq->vq.vdev, desc->flags);
+	}
 
 	if (flags & VRING_DESC_F_INDIRECT) {
 		dma_unmap_single(vring_dma_dev(vq),
-				 virtio64_to_cpu(vq->vq.vdev, desc->addr),
-				 virtio32_to_cpu(vq->vq.vdev, desc->len),
+				 addr, len,
 				 (flags & VRING_DESC_F_WRITE) ?
 				 DMA_FROM_DEVICE : DMA_TO_DEVICE);
 	} else {
 		dma_unmap_page(vring_dma_dev(vq),
-			       virtio64_to_cpu(vq->vq.vdev, desc->addr),
-			       virtio32_to_cpu(vq->vq.vdev, desc->len),
+			       addr, len,
 			       (flags & VRING_DESC_F_WRITE) ?
 			       DMA_FROM_DEVICE : DMA_TO_DEVICE);
 	}
@@ -235,8 +263,9 @@ static int vring_mapping_error(const struct vring_virtqueue *vq,
 	return dma_mapping_error(vring_dma_dev(vq), addr);
 }
 
-static struct vring_desc *alloc_indirect(struct virtqueue *_vq,
-					 unsigned int total_sg, gfp_t gfp)
+static struct vring_desc *alloc_indirect_split(struct virtqueue *_vq,
+					       unsigned int total_sg,
+					       gfp_t gfp)
 {
 	struct vring_desc *desc;
 	unsigned int i;
@@ -257,14 +286,32 @@ static struct vring_desc *alloc_indirect(struct virtqueue *_vq,
 	return desc;
 }
 
-static inline int virtqueue_add(struct virtqueue *_vq,
-				struct scatterlist *sgs[],
-				unsigned int total_sg,
-				unsigned int out_sgs,
-				unsigned int in_sgs,
-				void *data,
-				void *ctx,
-				gfp_t gfp)
+static struct vring_packed_desc *alloc_indirect_packed(struct virtqueue *_vq,
+						       unsigned int total_sg,
+						       gfp_t gfp)
+{
+	struct vring_packed_desc *desc;
+
+	/*
+	 * We require lowmem mappings for the descriptors because
+	 * otherwise virt_to_phys will give us bogus addresses in the
+	 * virtqueue.
+	 */
+	gfp &= ~__GFP_HIGHMEM;
+
+	desc = kmalloc(total_sg * sizeof(struct vring_packed_desc), gfp);
+
+	return desc;
+}
+
+static inline int virtqueue_add_split(struct virtqueue *_vq,
+				      struct scatterlist *sgs[],
+				      unsigned int total_sg,
+				      unsigned int out_sgs,
+				      unsigned int in_sgs,
+				      void *data,
+				      void *ctx,
+				      gfp_t gfp)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
 	struct scatterlist *sg;
@@ -303,7 +350,7 @@ static inline int virtqueue_add(struct virtqueue *_vq,
 	/* If the host supports indirect descriptor tables, and we have multiple
 	 * buffers, then go indirect. FIXME: tune this threshold */
 	if (vq->indirect && total_sg > 1 && vq->vq.num_free)
-		desc = alloc_indirect(_vq, total_sg, gfp);
+		desc = alloc_indirect_split(_vq, total_sg, gfp);
 	else {
 		desc = NULL;
 		WARN_ON_ONCE(total_sg > vq->vring.num && !vq->indirect);
@@ -437,6 +484,243 @@ static inline int virtqueue_add(struct virtqueue *_vq,
 	return -EIO;
 }
 
+static inline int virtqueue_add_packed(struct virtqueue *_vq,
+				       struct scatterlist *sgs[],
+				       unsigned int total_sg,
+				       unsigned int out_sgs,
+				       unsigned int in_sgs,
+				       void *data,
+				       void *ctx,
+				       gfp_t gfp)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+	struct vring_packed_desc *desc;
+	struct scatterlist *sg;
+	unsigned int i, n, descs_used, uninitialized_var(prev), err_idx;
+	__virtio16 uninitialized_var(head_flags), flags;
+	int head, wrap_counter;
+	bool indirect;
+
+	START_USE(vq);
+
+	BUG_ON(data == NULL);
+	BUG_ON(ctx && vq->indirect);
+
+	if (unlikely(vq->broken)) {
+		END_USE(vq);
+		return -EIO;
+	}
+
+	if (total_sg > 1 && !vq->chaining && !vq->indirect) {
+		END_USE(vq);
+		return -ENOTSUPP;
+	}
+
+#ifdef DEBUG
+	{
+		ktime_t now = ktime_get();
+
+		/* No kick or get, with .1 second between?  Warn. */
+		if (vq->last_add_time_valid)
+			WARN_ON(ktime_to_ms(ktime_sub(now, vq->last_add_time))
+					    > 100);
+		vq->last_add_time = now;
+		vq->last_add_time_valid = true;
+	}
+#endif
+
+	BUG_ON(total_sg == 0);
+
+	head = vq->free_head;
+	wrap_counter = vq->wrap_counter;
+
+	/* If the host supports indirect descriptor tables, and we have multiple
+	 * buffers, then go indirect. FIXME: tune this threshold */
+	if (vq->indirect && total_sg > 1 && vq->vq.num_free)
+		desc = alloc_indirect_packed(_vq, total_sg, gfp);
+	else {
+		desc = NULL;
+		WARN_ON_ONCE(total_sg > vq->vring.num && !vq->indirect);
+	}
+
+	if (desc) {
+		/* Use a single buffer which doesn't continue */
+		indirect = true;
+		/* Set up rest to use this indirect table. */
+		i = 0;
+		descs_used = 1;
+	} else {
+		indirect = false;
+		desc = vq->vring_packed.desc;
+		i = head;
+		descs_used = total_sg;
+
+		if (total_sg > 1 && !vq->chaining) {
+			END_USE(vq);
+			return -ENOTSUPP;
+		}
+	}
+
+	if (vq->vq.num_free < descs_used) {
+		pr_debug("Can't add buf len %i - avail = %i\n",
+			 descs_used, vq->vq.num_free);
+		/* FIXME: for historical reasons, we force a notify here if
+		 * there are outgoing parts to the buffer.  Presumably the
+		 * host should service the ring ASAP. */
+		if (out_sgs)
+			vq->notify(&vq->vq);
+		if (indirect)
+			kfree(desc);
+		END_USE(vq);
+		return -ENOSPC;
+	}
+
+	for (n = 0; n < out_sgs; n++) {
+		for (sg = sgs[n]; sg; sg = sg_next(sg)) {
+			dma_addr_t addr = vring_map_one_sg(vq, sg, DMA_TO_DEVICE);
+			if (vring_mapping_error(vq, addr))
+				goto unmap_release;
+
+			flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_NEXT |
+					VRING_DESC_F_AVAIL(vq->wrap_counter) |
+					VRING_DESC_F_USED(!vq->wrap_counter));
+			if (!indirect && i == head)
+				head_flags = flags;
+			else
+				desc[i].flags = flags;
+
+			desc[i].addr = cpu_to_virtio64(_vq->vdev, addr);
+			desc[i].len = cpu_to_virtio32(_vq->vdev, sg->length);
+			desc[i].id = cpu_to_virtio32(_vq->vdev, head);
+			prev = i;
+			i++;
+			if (!indirect && i >= vq->vring_packed.num) {
+				i = 0;
+				vq->wrap_counter ^= 1;
+			}
+		}
+	}
+	for (; n < (out_sgs + in_sgs); n++) {
+		for (sg = sgs[n]; sg; sg = sg_next(sg)) {
+			dma_addr_t addr = vring_map_one_sg(vq, sg, DMA_FROM_DEVICE);
+			if (vring_mapping_error(vq, addr))
+				goto unmap_release;
+
+			flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_NEXT |
+					VRING_DESC_F_WRITE |
+					VRING_DESC_F_AVAIL(vq->wrap_counter) |
+					VRING_DESC_F_USED(!vq->wrap_counter));
+			if (!indirect && i == head)
+				head_flags = flags;
+			else
+				desc[i].flags = flags;
+
+			desc[i].addr = cpu_to_virtio64(_vq->vdev, addr);
+			desc[i].len = cpu_to_virtio32(_vq->vdev, sg->length);
+			desc[i].id = cpu_to_virtio32(_vq->vdev, head);
+			prev = i;
+			i++;
+			if (!indirect && i >= vq->vring_packed.num) {
+				i = 0;
+				vq->wrap_counter ^= 1;
+			}
+		}
+	}
+	/* Last one doesn't continue. */
+	if (!indirect && (head + 1) % vq->vring_packed.num == i)
+		head_flags &= cpu_to_virtio16(_vq->vdev, ~VRING_DESC_F_NEXT);
+	else
+		desc[prev].flags &= cpu_to_virtio16(_vq->vdev, ~VRING_DESC_F_NEXT);
+
+	if (indirect) {
+		/* FIXME: to be implemented */
+
+		/* Now that the indirect table is filled in, map it. */
+		dma_addr_t addr = vring_map_single(
+			vq, desc, total_sg * sizeof(struct vring_packed_desc),
+			DMA_TO_DEVICE);
+		if (vring_mapping_error(vq, addr))
+			goto unmap_release;
+
+		head_flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_INDIRECT |
+					     VRING_DESC_F_AVAIL(wrap_counter) |
+					     VRING_DESC_F_USED(!wrap_counter));
+		vq->vring_packed.desc[head].addr = cpu_to_virtio64(_vq->vdev, addr);
+		vq->vring_packed.desc[head].len = cpu_to_virtio32(_vq->vdev,
+				total_sg * sizeof(struct vring_packed_desc));
+		vq->vring_packed.desc[head].id = cpu_to_virtio32(_vq->vdev, head);
+	}
+
+	/* We're using some buffers from the free list. */
+	vq->vq.num_free -= descs_used;
+
+	/* Update free pointer */
+	if (indirect) {
+		n = head + 1;
+		if (n >= vq->vring_packed.num) {
+			n = 0;
+			vq->wrap_counter ^= 1;
+		}
+		vq->free_head = n;
+	} else
+		vq->free_head = i;
+
+	/* Store token and indirect buffer state. */
+	vq->desc_state[head].num = descs_used;
+	vq->desc_state[head].data = data;
+	if (indirect)
+		vq->desc_state[head].indir_desc = desc;
+	else
+		vq->desc_state[head].indir_desc = ctx;
+
+	virtio_wmb(vq->weak_barriers);
+	vq->vring_packed.desc[head].flags = head_flags;
+	vq->num_added++;
+
+	pr_debug("Added buffer head %i to %p\n", head, vq);
+	END_USE(vq);
+
+	return 0;
+
+unmap_release:
+	err_idx = i;
+	i = head;
+
+	for (n = 0; n < total_sg; n++) {
+		if (i == err_idx)
+			break;
+		vring_unmap_one(vq, &desc[i]);
+		i++;
+		if (!indirect && i >= vq->vring_packed.num)
+			i = 0;
+	}
+
+	vq->wrap_counter = wrap_counter;
+
+	if (indirect)
+		kfree(desc);
+
+	END_USE(vq);
+	return -EIO;
+}
+
+static inline int virtqueue_add(struct virtqueue *_vq,
+				struct scatterlist *sgs[],
+				unsigned int total_sg,
+				unsigned int out_sgs,
+				unsigned int in_sgs,
+				void *data,
+				void *ctx,
+				gfp_t gfp)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+
+	return vq->packed ? virtqueue_add_packed(_vq, sgs, total_sg, out_sgs,
+						 in_sgs, data, ctx, gfp) :
+			    virtqueue_add_split(_vq, sgs, total_sg, out_sgs,
+						in_sgs, data, ctx, gfp);
+}
+
 /**
  * virtqueue_add_sgs - expose buffers to other end
  * @vq: the struct virtqueue we're talking about.
@@ -561,6 +845,12 @@ bool virtqueue_kick_prepare(struct virtqueue *_vq)
 	 * event. */
 	virtio_mb(vq->weak_barriers);
 
+	if (vq->packed) {
+		/* FIXME: to be implemented */
+		needs_kick = true;
+		goto out;
+	}
+
 	old = vq->avail_idx_shadow - vq->num_added;
 	new = vq->avail_idx_shadow;
 	vq->num_added = 0;
@@ -579,6 +869,8 @@ bool virtqueue_kick_prepare(struct virtqueue *_vq)
 	} else {
 		needs_kick = !(vq->vring.used->flags & cpu_to_virtio16(_vq->vdev, VRING_USED_F_NO_NOTIFY));
 	}
+
+out:
 	END_USE(vq);
 	return needs_kick;
 }
@@ -628,8 +920,8 @@ bool virtqueue_kick(struct virtqueue *vq)
 }
 EXPORT_SYMBOL_GPL(virtqueue_kick);
 
-static void detach_buf(struct vring_virtqueue *vq, unsigned int head,
-		       void **ctx)
+static void detach_buf_split(struct vring_virtqueue *vq, unsigned int head,
+			     void **ctx)
 {
 	unsigned int i, j;
 	__virtio16 nextflag = cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_NEXT);
@@ -677,29 +969,81 @@ static void detach_buf(struct vring_virtqueue *vq, unsigned int head,
 	}
 }
 
-static inline bool more_used(const struct vring_virtqueue *vq)
+static void detach_buf_packed(struct vring_virtqueue *vq, unsigned int head,
+			      void **ctx)
+{
+	struct vring_packed_desc *desc;
+	unsigned int i, j;
+
+	/* Clear data ptr. */
+	vq->desc_state[head].data = NULL;
+
+	i = head;
+
+	for (j = 0; j < vq->desc_state[head].num; j++) {
+		desc = &vq->vring_packed.desc[i];
+		vring_unmap_one(vq, desc);
+		i++;
+		if (i >= vq->vring_packed.num)
+			i = 0;
+	}
+
+	vq->vq.num_free += vq->desc_state[head].num;
+
+	if (vq->indirect) {
+		u32 len;
+
+		desc = vq->desc_state[head].indir_desc;
+		/* Free the indirect table, if any, now that it's unmapped. */
+		if (!desc)
+			return;
+
+		len = virtio32_to_cpu(vq->vq.vdev,
+				      vq->vring_packed.desc[head].len);
+
+		BUG_ON(!(vq->vring_packed.desc[head].flags &
+			 cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_INDIRECT)));
+		BUG_ON(len == 0 || len % sizeof(struct vring_packed_desc));
+
+		for (j = 0; j < len / sizeof(struct vring_packed_desc); j++)
+			vring_unmap_one(vq, &desc[j]);
+
+		kfree(desc);
+		vq->desc_state[head].indir_desc = NULL;
+	} else if (ctx) {
+		*ctx = vq->desc_state[head].indir_desc;
+	}
+}
+
+static inline bool more_used_split(const struct vring_virtqueue *vq)
 {
 	return vq->last_used_idx != virtio16_to_cpu(vq->vq.vdev, vq->vring.used->idx);
 }
 
-/**
- * virtqueue_get_buf - get the next used buffer
- * @vq: the struct virtqueue we're talking about.
- * @len: the length written into the buffer
- *
- * If the device wrote data into the buffer, @len will be set to the
- * amount written.  This means you don't need to clear the buffer
- * beforehand to ensure there's no data leakage in the case of short
- * writes.
- *
- * Caller must ensure we don't call this with other virtqueue
- * operations at the same time (except where noted).
- *
- * Returns NULL if there are no used buffers, or the "data" token
- * handed to virtqueue_add_*().
- */
-void *virtqueue_get_buf_ctx(struct virtqueue *_vq, unsigned int *len,
-			    void **ctx)
+static inline bool more_used_packed(const struct vring_virtqueue *vq)
+{
+	u16 last_used, flags;
+	bool avail, used;
+
+	if (vq->vq.num_free == vq->vring.num)
+		return false;
+
+	last_used = vq->last_used_idx;
+	flags = virtio16_to_cpu(vq->vq.vdev,
+				vq->vring_packed.desc[last_used].flags);
+	avail = flags & VRING_DESC_F_AVAIL(1);
+	used = flags & VRING_DESC_F_USED(1);
+
+	return avail == used;
+}
+
+static inline bool more_used(const struct vring_virtqueue *vq)
+{
+	return vq->packed ? more_used_packed(vq) : more_used_split(vq);
+}
+
+void *virtqueue_get_buf_ctx_split(struct virtqueue *_vq, unsigned int *len,
+				  void **ctx)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
 	void *ret;
@@ -735,9 +1079,9 @@ void *virtqueue_get_buf_ctx(struct virtqueue *_vq, unsigned int *len,
 		return NULL;
 	}
 
-	/* detach_buf clears data, so grab it now. */
+	/* detach_buf_split clears data, so grab it now. */
 	ret = vq->desc_state[i].data;
-	detach_buf(vq, i, ctx);
+	detach_buf_split(vq, i, ctx);
 	vq->last_used_idx++;
 	/* If we expect an interrupt for the next entry, tell host
 	 * by writing event index and flush out the write before
@@ -754,6 +1098,87 @@ void *virtqueue_get_buf_ctx(struct virtqueue *_vq, unsigned int *len,
 	END_USE(vq);
 	return ret;
 }
+
+void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq, unsigned int *len,
+				   void **ctx)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+	void *ret;
+	unsigned int i;
+	u16 last_used;
+
+	START_USE(vq);
+
+	if (unlikely(vq->broken)) {
+		END_USE(vq);
+		return NULL;
+	}
+
+	if (!more_used(vq)) {
+		pr_debug("No more buffers in queue\n");
+		END_USE(vq);
+		return NULL;
+	}
+
+	/* Only get used array entries after they have been exposed by host. */
+	virtio_rmb(vq->weak_barriers);
+
+	last_used = vq->last_used_idx;
+
+	i = virtio32_to_cpu(_vq->vdev, vq->vring_packed.desc[last_used].id);
+	*len = virtio32_to_cpu(_vq->vdev, vq->vring_packed.desc[last_used].len);
+
+	if (unlikely(i >= vq->vring_packed.num)) {
+		BAD_RING(vq, "id %u out of range\n", i);
+		return NULL;
+	}
+	if (unlikely(!vq->desc_state[i].data)) {
+		BAD_RING(vq, "id %u is not a head!\n", i);
+		return NULL;
+	}
+
+	/* detach_buf_packed clears data, so grab it now. */
+	ret = vq->desc_state[i].data;
+	detach_buf_packed(vq, i, ctx);
+
+	vq->last_used_idx += vq->desc_state[i].num;
+	if (vq->last_used_idx >= vq->vring_packed.num)
+		vq->last_used_idx %= vq->vring_packed.num;
+
+	// FIXME: implement the desc event support
+
+#ifdef DEBUG
+	vq->last_add_time_valid = false;
+#endif
+
+	END_USE(vq);
+	return ret;
+}
+
+/**
+ * virtqueue_get_buf - get the next used buffer
+ * @vq: the struct virtqueue we're talking about.
+ * @len: the length written into the buffer
+ *
+ * If the device wrote data into the buffer, @len will be set to the
+ * amount written.  This means you don't need to clear the buffer
+ * beforehand to ensure there's no data leakage in the case of short
+ * writes.
+ *
+ * Caller must ensure we don't call this with other virtqueue
+ * operations at the same time (except where noted).
+ *
+ * Returns NULL if there are no used buffers, or the "data" token
+ * handed to virtqueue_add_*().
+ */
+void *virtqueue_get_buf_ctx(struct virtqueue *_vq, unsigned int *len,
+			    void **ctx)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+
+	return vq->packed ? virtqueue_get_buf_ctx_packed(_vq, len, ctx) :
+			    virtqueue_get_buf_ctx_split(_vq, len, ctx);
+}
 EXPORT_SYMBOL_GPL(virtqueue_get_buf_ctx);
 
 void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len)
@@ -761,6 +1186,24 @@ void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len)
 	return virtqueue_get_buf_ctx(_vq, len, NULL);
 }
 EXPORT_SYMBOL_GPL(virtqueue_get_buf);
+
+static void virtqueue_disable_cb_split(struct virtqueue *_vq)
+{
+	struct vring_virtqueue *vq = to_vvq(_vq);
+
+	if (!(vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT)) {
+		vq->avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT;
+		if (!vq->event)
+			vq->vring.avail->flags = cpu_to_virtio16(_vq->vdev,
+							vq->avail_flags_shadow);
+	}
+}
+
+static void virtqueue_disable_cb_packed(struct virtqueue *_vq)
+{
+	// FIXME: to be implemented
+}
+
 /**
  * virtqueue_disable_cb - disable callbacks
  * @vq: the struct virtqueue we're talking about.
@@ -774,12 +1217,10 @@ void virtqueue_disable_cb(struct virtqueue *_vq)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
 
-	if (!(vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT)) {
-		vq->avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT;
-		if (!vq->event)
-			vq->vring.avail->flags = cpu_to_virtio16(_vq->vdev, vq->avail_flags_shadow);
-	}
-
+	if (vq->packed)
+		virtqueue_disable_cb_packed(_vq);
+	else
+		virtqueue_disable_cb_split(_vq);
 }
 EXPORT_SYMBOL_GPL(virtqueue_disable_cb);
 
@@ -802,6 +1243,12 @@ unsigned virtqueue_enable_cb_prepare(struct virtqueue *_vq)
 
 	START_USE(vq);
 
+	if (vq->packed) {
+		// FIXME: to be implemented
+		last_used_idx = vq->last_used_idx;
+		goto out;
+	}
+
 	/* We optimistically turn back on interrupts, then check if there was
 	 * more to do. */
 	/* Depending on the VIRTIO_RING_F_EVENT_IDX feature, we need to
@@ -813,6 +1260,7 @@ unsigned virtqueue_enable_cb_prepare(struct virtqueue *_vq)
 			vq->vring.avail->flags = cpu_to_virtio16(_vq->vdev, vq->avail_flags_shadow);
 	}
 	vring_used_event(&vq->vring) = cpu_to_virtio16(_vq->vdev, last_used_idx = vq->last_used_idx);
+out:
 	END_USE(vq);
 	return last_used_idx;
 }
@@ -832,6 +1280,12 @@ bool virtqueue_poll(struct virtqueue *_vq, unsigned last_used_idx)
 	struct vring_virtqueue *vq = to_vvq(_vq);
 
 	virtio_mb(vq->weak_barriers);
+	if (vq->packed) {
+		u16 flags = virtio16_to_cpu(vq->vq.vdev,
+				vq->vring_packed.desc[last_used_idx].flags);
+		return !(flags & VRING_DESC_F_AVAIL(1)) ==
+		       !(flags & VRING_DESC_F_USED(1));
+	}
 	return (u16)last_used_idx != virtio16_to_cpu(_vq->vdev, vq->vring.used->idx);
 }
 EXPORT_SYMBOL_GPL(virtqueue_poll);
@@ -874,6 +1328,11 @@ bool virtqueue_enable_cb_delayed(struct virtqueue *_vq)
 
 	START_USE(vq);
 
+	if (vq->packed) {
+		// FIXME: to be implemented
+		goto out;
+	}
+
 	/* We optimistically turn back on interrupts, then check if there was
 	 * more to do. */
 	/* Depending on the VIRTIO_RING_F_USED_EVENT_IDX feature, we need to
@@ -896,6 +1355,7 @@ bool virtqueue_enable_cb_delayed(struct virtqueue *_vq)
 		return false;
 	}
 
+out:
 	END_USE(vq);
 	return true;
 }
@@ -922,14 +1382,20 @@ void *virtqueue_detach_unused_buf(struct virtqueue *_vq)
 			continue;
 		/* detach_buf clears data, so grab it now. */
 		buf = vq->desc_state[i].data;
-		detach_buf(vq, i, NULL);
-		vq->avail_idx_shadow--;
-		vq->vring.avail->idx = cpu_to_virtio16(_vq->vdev, vq->avail_idx_shadow);
+		if (vq->packed)
+			detach_buf_packed(vq, i, NULL);
+		else {
+			detach_buf_split(vq, i, NULL);
+			vq->avail_idx_shadow--;
+			vq->vring.avail->idx = cpu_to_virtio16(_vq->vdev,
+							vq->avail_idx_shadow);
+		}
 		END_USE(vq);
 		return buf;
 	}
 	/* That should have freed everything. */
-	BUG_ON(vq->vq.num_free != vq->vring.num);
+	BUG_ON(vq->vq.num_free != (vq->packed ? vq->vring_packed.num :
+						vq->vring.num));
 
 	END_USE(vq);
 	return NULL;
@@ -957,7 +1423,8 @@ irqreturn_t vring_interrupt(int irq, void *_vq)
 EXPORT_SYMBOL_GPL(vring_interrupt);
 
 struct virtqueue *__vring_new_virtqueue(unsigned int index,
-					struct vring vring,
+					union vring_union vring,
+					bool packed,
 					struct virtio_device *vdev,
 					bool weak_barriers,
 					bool context,
@@ -965,19 +1432,20 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
 					void (*callback)(struct virtqueue *),
 					const char *name)
 {
-	unsigned int i;
+	unsigned int num, i;
 	struct vring_virtqueue *vq;
 
-	vq = kmalloc(sizeof(*vq) + vring.num * sizeof(struct vring_desc_state),
+	num = packed ? vring.vring_packed.num : vring.vring_split.num;
+
+	vq = kmalloc(sizeof(*vq) + num * sizeof(struct vring_desc_state),
 		     GFP_KERNEL);
 	if (!vq)
 		return NULL;
 
-	vq->vring = vring;
 	vq->vq.callback = callback;
 	vq->vq.vdev = vdev;
 	vq->vq.name = name;
-	vq->vq.num_free = vring.num;
+	vq->vq.num_free = num;
 	vq->vq.index = index;
 	vq->we_own_ring = false;
 	vq->queue_dma_addr = 0;
@@ -986,9 +1454,8 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
 	vq->weak_barriers = weak_barriers;
 	vq->broken = false;
 	vq->last_used_idx = 0;
-	vq->avail_flags_shadow = 0;
-	vq->avail_idx_shadow = 0;
 	vq->num_added = 0;
+	vq->packed = packed;
 	list_add_tail(&vq->vq.list, &vdev->vqs);
 #ifdef DEBUG
 	vq->in_use = false;
@@ -999,18 +1466,41 @@ struct virtqueue *__vring_new_virtqueue(unsigned int index,
 		!context;
 	vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);
 
+	if (vq->packed) {
+		vq->vring_packed = vring.vring_packed;
+		vq->free_head = 0;
+		vq->wrap_counter = 1;
+
+#if 0
+		vq->chaining = virtio_has_feature(vdev,
+						  VIRTIO_RING_F_LIST_DESC);
+#else
+		vq->chaining = true;
+#endif
+	} else {
+		vq->vring = vring.vring_split;
+		vq->avail_flags_shadow = 0;
+		vq->avail_idx_shadow = 0;
+
+		/* Put everything in free lists. */
+		vq->free_head = 0;
+		for (i = 0; i < num-1; i++)
+			vq->vring.desc[i].next = cpu_to_virtio16(vdev, i + 1);
+	}
+
 	/* No callback?  Tell other side not to bother us. */
 	if (!callback) {
-		vq->avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT;
-		if (!vq->event)
-			vq->vring.avail->flags = cpu_to_virtio16(vdev, vq->avail_flags_shadow);
+		if (packed) {
+			// FIXME: to be implemented
+		} else {
+			vq->avail_flags_shadow |= VRING_AVAIL_F_NO_INTERRUPT;
+			if (!vq->event)
+				vq->vring.avail->flags = cpu_to_virtio16(vdev,
+						vq->avail_flags_shadow);
+		}
 	}
 
-	/* Put everything in free lists. */
-	vq->free_head = 0;
-	for (i = 0; i < vring.num-1; i++)
-		vq->vring.desc[i].next = cpu_to_virtio16(vdev, i + 1);
-	memset(vq->desc_state, 0, vring.num * sizeof(struct vring_desc_state));
+	memset(vq->desc_state, 0, num * sizeof(struct vring_desc_state));
 
 	return &vq->vq;
 }
@@ -1058,6 +1548,14 @@ static void vring_free_queue(struct virtio_device *vdev, size_t size,
 	}
 }
 
+static inline int
+__vring_size(unsigned int num, unsigned long align, bool packed)
+{
+	if (packed)
+		return vring_packed_size(num, align);
+	return vring_size(num, align);
+}
+
 struct virtqueue *vring_create_virtqueue(
 	unsigned int index,
 	unsigned int num,
@@ -1074,7 +1572,8 @@ struct virtqueue *vring_create_virtqueue(
 	void *queue = NULL;
 	dma_addr_t dma_addr;
 	size_t queue_size_in_bytes;
-	struct vring vring;
+	union vring_union vring;
+	bool packed;
 
 	/* We assume num is a power of 2. */
 	if (num & (num - 1)) {
@@ -1082,9 +1581,13 @@ struct virtqueue *vring_create_virtqueue(
 		return NULL;
 	}
 
+	packed = virtio_has_feature(vdev, VIRTIO_F_RING_PACKED);
+
 	/* TODO: allocate each queue chunk individually */
-	for (; num && vring_size(num, vring_align) > PAGE_SIZE; num /= 2) {
-		queue = vring_alloc_queue(vdev, vring_size(num, vring_align),
+	for (; num && __vring_size(num, vring_align, packed) > PAGE_SIZE;
+			num /= 2) {
+		queue = vring_alloc_queue(vdev, __vring_size(num, vring_align,
+							     packed),
 					  &dma_addr,
 					  GFP_KERNEL|__GFP_NOWARN|__GFP_ZERO);
 		if (queue)
@@ -1096,17 +1599,21 @@ struct virtqueue *vring_create_virtqueue(
 
 	if (!queue) {
 		/* Try to get a single page. You are my only hope! */
-		queue = vring_alloc_queue(vdev, vring_size(num, vring_align),
+		queue = vring_alloc_queue(vdev, __vring_size(num, vring_align,
+							     packed),
 					  &dma_addr, GFP_KERNEL|__GFP_ZERO);
 	}
 	if (!queue)
 		return NULL;
 
-	queue_size_in_bytes = vring_size(num, vring_align);
-	vring_init(&vring, num, queue, vring_align);
+	queue_size_in_bytes = __vring_size(num, vring_align, packed);
+	if (packed)
+		vring_packed_init(&vring.vring_packed, num, queue, vring_align);
+	else
+		vring_init(&vring.vring_split, num, queue, vring_align);
 
-	vq = __vring_new_virtqueue(index, vring, vdev, weak_barriers, context,
-				   notify, callback, name);
+	vq = __vring_new_virtqueue(index, vring, packed, vdev, weak_barriers,
+				   context, notify, callback, name);
 	if (!vq) {
 		vring_free_queue(vdev, queue_size_in_bytes, queue,
 				 dma_addr);
@@ -1132,10 +1639,17 @@ struct virtqueue *vring_new_virtqueue(unsigned int index,
 				      void (*callback)(struct virtqueue *vq),
 				      const char *name)
 {
-	struct vring vring;
-	vring_init(&vring, num, pages, vring_align);
-	return __vring_new_virtqueue(index, vring, vdev, weak_barriers, context,
-				     notify, callback, name);
+	union vring_union vring;
+	bool packed;
+
+	packed = virtio_has_feature(vdev, VIRTIO_F_RING_PACKED);
+	if (packed)
+		vring_packed_init(&vring.vring_packed, num, pages, vring_align);
+	else
+		vring_init(&vring.vring_split, num, pages, vring_align);
+
+	return __vring_new_virtqueue(index, vring, packed, vdev, weak_barriers,
+				     context, notify, callback, name);
 }
 EXPORT_SYMBOL_GPL(vring_new_virtqueue);
 
@@ -1145,7 +1659,9 @@ void vring_del_virtqueue(struct virtqueue *_vq)
 
 	if (vq->we_own_ring) {
 		vring_free_queue(vq->vq.vdev, vq->queue_size_in_bytes,
-				 vq->vring.desc, vq->queue_dma_addr);
+				 vq->packed ? (void *)vq->vring_packed.desc :
+					      (void *)vq->vring.desc,
+				 vq->queue_dma_addr);
 	}
 	list_del(&_vq->list);
 	kfree(vq);
@@ -1159,14 +1675,18 @@ void vring_transport_features(struct virtio_device *vdev)
 
 	for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++) {
 		switch (i) {
+#if 0 // FIXME: to be implemented
 		case VIRTIO_RING_F_INDIRECT_DESC:
 			break;
+#endif
 		case VIRTIO_RING_F_EVENT_IDX:
 			break;
 		case VIRTIO_F_VERSION_1:
 			break;
 		case VIRTIO_F_IOMMU_PLATFORM:
 			break;
+		case VIRTIO_F_RING_PACKED:
+			break;
 		default:
 			/* We don't understand this bit. */
 			__virtio_clear_bit(vdev, i);
@@ -1187,7 +1707,7 @@ unsigned int virtqueue_get_vring_size(struct virtqueue *_vq)
 
 	struct vring_virtqueue *vq = to_vvq(_vq);
 
-	return vq->vring.num;
+	return vq->packed ? vq->vring_packed.num : vq->vring.num;
 }
 EXPORT_SYMBOL_GPL(virtqueue_get_vring_size);
 
@@ -1224,6 +1744,7 @@ dma_addr_t virtqueue_get_desc_addr(struct virtqueue *_vq)
 }
 EXPORT_SYMBOL_GPL(virtqueue_get_desc_addr);
 
+/* Only available for split ring */
 dma_addr_t virtqueue_get_avail_addr(struct virtqueue *_vq)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
@@ -1235,6 +1756,7 @@ dma_addr_t virtqueue_get_avail_addr(struct virtqueue *_vq)
 }
 EXPORT_SYMBOL_GPL(virtqueue_get_avail_addr);
 
+/* Only available for split ring */
 dma_addr_t virtqueue_get_used_addr(struct virtqueue *_vq)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
@@ -1246,6 +1768,7 @@ dma_addr_t virtqueue_get_used_addr(struct virtqueue *_vq)
 }
 EXPORT_SYMBOL_GPL(virtqueue_get_used_addr);
 
+/* Only available for split ring */
 const struct vring *virtqueue_get_vring(struct virtqueue *vq)
 {
 	return &to_vvq(vq)->vring;
diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index bbf32524ab27..a0075894ad16 100644
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h
@@ -60,6 +60,11 @@ static inline void virtio_store_mb(bool weak_barriers,
 struct virtio_device;
 struct virtqueue;
 
+union vring_union {
+	struct vring vring_split;
+	struct vring_packed vring_packed;
+};
+
 /*
  * Creates a virtqueue and allocates the descriptor ring.  If
  * may_reduce_num is set, then this may allocate a smaller ring than
@@ -79,7 +84,8 @@ struct virtqueue *vring_create_virtqueue(unsigned int index,
 
 /* Creates a virtqueue with a custom layout. */
 struct virtqueue *__vring_new_virtqueue(unsigned int index,
-					struct vring vring,
+					union vring_union vring,
+					bool packed,
 					struct virtio_device *vdev,
 					bool weak_barriers,
 					bool ctx,
-- 
2.14.1