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;
Subject: Re: [RFC v2] virtio: support packed ring
To:     Tiwei Bie <tiwei.bie@intel.com>, mst@redhat.com, wexu@redhat.com,
        virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, netdev@vger.kernel.org
Cc:     jfreimann@redhat.com
References: <20180401141216.8969-1-tiwei.bie@intel.com>
From:   Jason Wang <jasowang@redhat.com>
Message-ID: <5cf4d5d6-c416-28af-0568-750e9f654710@redhat.com>
Date:   Tue, 10 Apr 2018 10:55:25 +0800
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.6.0
MIME-Version: 1.0
In-Reply-To: <20180401141216.8969-1-tiwei.bie@intel.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 8bit
Content-Language: en-US
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


On 2018年04月01日 22:12, Tiwei Bie wrote:
> Hello everyone,
>
> This RFC implements packed ring support for virtio driver.
>
> The code was tested with DPDK vhost (testpmd/vhost-PMD) implemented
> by Jens at http://dpdk.org/ml/archives/dev/2018-January/089417.html
> Minor changes are needed for the vhost code, e.g. to kick the guest.
>
> TODO:
> - Refinements and bug fixes;
> - Split into small patches;
> - Test indirect descriptor support;
> - Test/fix event suppression support;
> - Test devices other than net;
>
> RFC v1 -> RFC v2:
> - Add indirect descriptor support - compile test only;
> - Add event suppression supprt - compile test only;
> - Move vring_packed_init() out of uapi (Jason, MST);
> - Merge two loops into one in virtqueue_add_packed() (Jason);
> - Split vring_unmap_one() for packed ring and split ring (Jason);
> - Avoid using '%' operator (Jason);
> - Rename free_head -> next_avail_idx (Jason);
> - Add comments for virtio_wmb() in virtqueue_add_packed() (Jason);
> - Some other refinements and bug fixes;
>
> Thanks!

Will try to review this later.

But it would be better if you can split it (more than 1000 lines is too 
big to be reviewed easily). E.g you can at least split it into three 
patches, new structures, datapath, and event suppression.

Thanks


>
> Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
> ---
>   drivers/virtio/virtio_ring.c       | 1094 +++++++++++++++++++++++++++++-------
>   include/linux/virtio_ring.h        |    8 +-
>   include/uapi/linux/virtio_config.h |   12 +-
>   include/uapi/linux/virtio_ring.h   |   61 ++
>   4 files changed, 980 insertions(+), 195 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 71458f493cf8..0515dca34d77 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -58,14 +58,15 @@
>   
>   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;
> +	/* Is this a packed ring? */
> +	bool packed;
>   
>   	/* Can we use weak barriers? */
>   	bool weak_barriers;
> @@ -79,19 +80,45 @@ struct vring_virtqueue {
>   	/* Host publishes avail event idx */
>   	bool event;
>   
> -	/* Head of free buffer list. */
> -	unsigned int free_head;
>   	/* Number we've added since last sync. */
>   	unsigned int num_added;
>   
>   	/* Last used index we've seen. */
>   	u16 last_used_idx;
>   
> -	/* Last written value to avail->flags */
> -	u16 avail_flags_shadow;
> +	union {
> +		/* Available for split ring */
> +		struct {
> +			/* Actual memory layout for this queue. */
> +			struct vring vring;
>   
> -	/* Last written value to avail->idx in guest byte order */
> -	u16 avail_idx_shadow;
> +			/* Head of free buffer list. */
> +			unsigned int free_head;
> +
> +			/* 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;
> +
> +			/* Driver ring wrap counter. */
> +			u8 wrap_counter;
> +
> +			/* Index of the next avail descriptor. */
> +			unsigned int next_avail_idx;
> +
> +			/* Last written value to driver->flags in
> +			 * guest byte order. */
> +			u16 event_flags_shadow;
> +		};
> +	};
>   
>   	/* How to notify other side. FIXME: commonalize hcalls! */
>   	bool (*notify)(struct virtqueue *vq);
> @@ -201,8 +228,33 @@ 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_split(const struct vring_virtqueue *vq,
> +				  struct vring_desc *desc)
> +{
> +	u16 flags;
> +
> +	if (!vring_use_dma_api(vq->vq.vdev))
> +		return;
> +
> +	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),
> +				 (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),
> +			       (flags & VRING_DESC_F_WRITE) ?
> +			       DMA_FROM_DEVICE : DMA_TO_DEVICE);
> +	}
> +}
> +
> +static void vring_unmap_one_packed(const struct vring_virtqueue *vq,
> +				   struct vring_packed_desc *desc)
>   {
>   	u16 flags;
>   
> @@ -235,8 +287,9 @@ 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 +310,32 @@ 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 +374,7 @@ 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);
> @@ -424,7 +495,7 @@ static inline int virtqueue_add(struct virtqueue *_vq,
>   	for (n = 0; n < total_sg; n++) {
>   		if (i == err_idx)
>   			break;
> -		vring_unmap_one(vq, &desc[i]);
> +		vring_unmap_one_split(vq, &desc[i]);
>   		i = virtio16_to_cpu(_vq->vdev, vq->vring.desc[i].next);
>   	}
>   
> @@ -435,6 +506,210 @@ 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;
> +	}
> +
> +#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->next_avail_idx;
> +	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_packed.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 (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 + in_sgs; n++) {
> +		for (sg = sgs[n]; sg; sg = sg_next(sg)) {
> +			dma_addr_t addr = vring_map_one_sg(vq, sg, n < out_sgs ?
> +						DMA_TO_DEVICE : DMA_FROM_DEVICE);
> +			if (vring_mapping_error(vq, addr))
> +				goto unmap_release;
> +
> +			flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_NEXT |
> +					(n < out_sgs ? 0 : 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 (total_sg == 1)
> +		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) {
> +		/* 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->next_avail_idx = n;
> +	} else
> +		vq->next_avail_idx = 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;
> +
> +	/* A driver MUST NOT make the first descriptor in the list
> +	 * available before all subsequent descriptors comprising
> +	 * the list are made available. */
> +	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_packed(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.
> @@ -537,18 +812,7 @@ int virtqueue_add_inbuf_ctx(struct virtqueue *vq,
>   }
>   EXPORT_SYMBOL_GPL(virtqueue_add_inbuf_ctx);
>   
> -/**
> - * virtqueue_kick_prepare - first half of split virtqueue_kick call.
> - * @vq: the struct virtqueue
> - *
> - * Instead of virtqueue_kick(), you can do:
> - *	if (virtqueue_kick_prepare(vq))
> - *		virtqueue_notify(vq);
> - *
> - * This is sometimes useful because the virtqueue_kick_prepare() needs
> - * to be serialized, but the actual virtqueue_notify() call does not.
> - */
> -bool virtqueue_kick_prepare(struct virtqueue *_vq)
> +static bool virtqueue_kick_prepare_split(struct virtqueue *_vq)
>   {
>   	struct vring_virtqueue *vq = to_vvq(_vq);
>   	u16 new, old;
> @@ -580,6 +844,62 @@ bool virtqueue_kick_prepare(struct virtqueue *_vq)
>   	END_USE(vq);
>   	return needs_kick;
>   }
> +
> +static bool virtqueue_kick_prepare_packed(struct virtqueue *_vq)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	u16 new, old, off_wrap;
> +	bool needs_kick;
> +
> +	START_USE(vq);
> +	/* We need to expose the new flags value before checking notification
> +	 * suppressions. */
> +	virtio_mb(vq->weak_barriers);
> +
> +	old = vq->next_avail_idx - vq->num_added;
> +	new = vq->next_avail_idx;
> +	vq->num_added = 0;
> +
> +#ifdef DEBUG
> +	if (vq->last_add_time_valid) {
> +		WARN_ON(ktime_to_ms(ktime_sub(ktime_get(),
> +					      vq->last_add_time)) > 100);
> +	}
> +	vq->last_add_time_valid = false;
> +#endif
> +
> +	off_wrap = virtio16_to_cpu(_vq->vdev, vq->vring_packed.device->off_wrap);
> +
> +	if (vq->event) {
> +		// FIXME: fix this!
> +		needs_kick = ((off_wrap >> 15) == vq->wrap_counter) &&
> +			     vring_need_event(off_wrap & ~(1<<15), new, old);
> +	} else {
> +		needs_kick = (vq->vring_packed.device->flags !=
> +			      cpu_to_virtio16(_vq->vdev, VRING_EVENT_F_DISABLE));
> +	}
> +	END_USE(vq);
> +	return needs_kick;
> +}
> +
> +/**
> + * virtqueue_kick_prepare - first half of split virtqueue_kick call.
> + * @vq: the struct virtqueue
> + *
> + * Instead of virtqueue_kick(), you can do:
> + *	if (virtqueue_kick_prepare(vq))
> + *		virtqueue_notify(vq);
> + *
> + * This is sometimes useful because the virtqueue_kick_prepare() needs
> + * to be serialized, but the actual virtqueue_notify() call does not.
> + */
> +bool virtqueue_kick_prepare(struct virtqueue *_vq)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +
> +	return vq->packed ? virtqueue_kick_prepare_packed(_vq) :
> +			    virtqueue_kick_prepare_split(_vq);
> +}
>   EXPORT_SYMBOL_GPL(virtqueue_kick_prepare);
>   
>   /**
> @@ -626,8 +946,8 @@ 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);
> @@ -639,12 +959,12 @@ static void detach_buf(struct vring_virtqueue *vq, unsigned int head,
>   	i = head;
>   
>   	while (vq->vring.desc[i].flags & nextflag) {
> -		vring_unmap_one(vq, &vq->vring.desc[i]);
> +		vring_unmap_one_split(vq, &vq->vring.desc[i]);
>   		i = virtio16_to_cpu(vq->vq.vdev, vq->vring.desc[i].next);
>   		vq->vq.num_free++;
>   	}
>   
> -	vring_unmap_one(vq, &vq->vring.desc[i]);
> +	vring_unmap_one_split(vq, &vq->vring.desc[i]);
>   	vq->vring.desc[i].next = cpu_to_virtio16(vq->vq.vdev, vq->free_head);
>   	vq->free_head = head;
>   
> @@ -666,7 +986,7 @@ static void detach_buf(struct vring_virtqueue *vq, unsigned int head,
>   		BUG_ON(len == 0 || len % sizeof(struct vring_desc));
>   
>   		for (j = 0; j < len / sizeof(struct vring_desc); j++)
> -			vring_unmap_one(vq, &indir_desc[j]);
> +			vring_unmap_one_split(vq, &indir_desc[j]);
>   
>   		kfree(indir_desc);
>   		vq->desc_state[head].indir_desc = NULL;
> @@ -675,11 +995,207 @@ static void detach_buf(struct vring_virtqueue *vq, unsigned int head,
>   	}
>   }
>   
> -static inline bool more_used(const struct vring_virtqueue *vq)
> +static int 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_packed(vq, desc);
> +		desc->flags = 0x0;
> +		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)
> +			goto out;
> +
> +		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_packed(vq, &desc[j]);
> +
> +		kfree(desc);
> +		vq->desc_state[head].indir_desc = NULL;
> +	} else if (ctx) {
> +		*ctx = vq->desc_state[head].indir_desc;
> +	}
> +
> +out:
> +	return vq->desc_state[head].num;
> +}
> +
> +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);
>   }
>   
> +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_packed.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;
> +	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 & (vq->vring.num - 1));
> +	i = virtio32_to_cpu(_vq->vdev, vq->vring.used->ring[last_used].id);
> +	*len = virtio32_to_cpu(_vq->vdev, vq->vring.used->ring[last_used].len);
> +
> +	if (unlikely(i >= vq->vring.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_split clears data, so grab it now. */
> +	ret = vq->desc_state[i].data;
> +	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
> +	 * the read in the next get_buf call. */
> +	if (!(vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT))
> +		virtio_store_mb(vq->weak_barriers,
> +				&vring_used_event(&vq->vring),
> +				cpu_to_virtio16(_vq->vdev, vq->last_used_idx));
> +
> +#ifdef DEBUG
> +	vq->last_add_time_valid = false;
> +#endif
> +
> +	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);
> +	uint16_t wrap_counter;
> +	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 elements 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;
> +
> +	wrap_counter = vq->wrap_counter;
> +	if (vq->last_used_idx > vq->next_avail_idx)
> +		wrap_counter ^= 1;
> +
> +	/* If we expect an interrupt for the next entry, tell host
> +	 * by writing event index and flush out the write before
> +	 * the read in the next get_buf call. */
> +	if (vq->event_flags_shadow == VRING_EVENT_F_DESC)
> +		virtio_store_mb(vq->weak_barriers,
> +				&vq->vring_packed.driver->off_wrap,
> +				cpu_to_virtio16(_vq->vdev, vq->last_used_idx |
> +						wrap_counter << 15));
> +
> +#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.
> @@ -700,57 +1216,9 @@ void *virtqueue_get_buf_ctx(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 & (vq->vring.num - 1));
> -	i = virtio32_to_cpu(_vq->vdev, vq->vring.used->ring[last_used].id);
> -	*len = virtio32_to_cpu(_vq->vdev, vq->vring.used->ring[last_used].len);
> -
> -	if (unlikely(i >= vq->vring.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 clears data, so grab it now. */
> -	ret = vq->desc_state[i].data;
> -	detach_buf(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
> -	 * the read in the next get_buf call. */
> -	if (!(vq->avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT))
> -		virtio_store_mb(vq->weak_barriers,
> -				&vring_used_event(&vq->vring),
> -				cpu_to_virtio16(_vq->vdev, vq->last_used_idx));
> -
> -#ifdef DEBUG
> -	vq->last_add_time_valid = false;
> -#endif
> -
> -	END_USE(vq);
> -	return ret;
> +	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);
>   
> @@ -759,6 +1227,29 @@ 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)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +
> +	if (vq->event_flags_shadow != VRING_EVENT_F_DISABLE) {
> +		vq->event_flags_shadow = VRING_EVENT_F_DISABLE;
> +		vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev,
> +							vq->event_flags_shadow);
> +	}
> +}
> +
>   /**
>    * virtqueue_disable_cb - disable callbacks
>    * @vq: the struct virtqueue we're talking about.
> @@ -772,15 +1263,66 @@ 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);
>   
> +static unsigned virtqueue_enable_cb_prepare_split(struct virtqueue *_vq)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	u16 last_used_idx;
> +
> +	START_USE(vq);
> +
> +	/* 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
> +	 * either clear the flags bit or point the event index at the next
> +	 * entry. Always do both to keep code simple. */
> +	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);
> +	}
> +	vring_used_event(&vq->vring) = cpu_to_virtio16(_vq->vdev, last_used_idx = vq->last_used_idx);
> +	END_USE(vq);
> +	return last_used_idx;
> +}
> +
> +static unsigned virtqueue_enable_cb_prepare_packed(struct virtqueue *_vq)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	u16 last_used_idx, wrap_counter, off_wrap;
> +
> +	START_USE(vq);
> +
> +	last_used_idx = vq->last_used_idx;
> +	wrap_counter = vq->wrap_counter;
> +
> +	if (last_used_idx > vq->next_avail_idx)
> +		wrap_counter ^= 1;
> +
> +	off_wrap = last_used_idx | (wrap_counter << 15);
> +
> +	/* 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
> +	 * either clear the flags bit or point the event index at the next
> +	 * entry. Always do both to keep code simple. */
> +	if (vq->event_flags_shadow == VRING_EVENT_F_DISABLE) {
> +		vq->event_flags_shadow = vq->event ? VRING_EVENT_F_DESC:
> +						     VRING_EVENT_F_ENABLE;
> +		vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev,
> +							vq->event_flags_shadow);
> +	}
> +	vq->vring_packed.driver->off_wrap = cpu_to_virtio16(_vq->vdev, off_wrap);
> +	END_USE(vq);
> +	return last_used_idx;
> +}
> +
>   /**
>    * virtqueue_enable_cb_prepare - restart callbacks after disable_cb
>    * @vq: the struct virtqueue we're talking about.
> @@ -796,26 +1338,34 @@ EXPORT_SYMBOL_GPL(virtqueue_disable_cb);
>   unsigned virtqueue_enable_cb_prepare(struct virtqueue *_vq)
>   {
>   	struct vring_virtqueue *vq = to_vvq(_vq);
> -	u16 last_used_idx;
>   
> -	START_USE(vq);
> -
> -	/* 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
> -	 * either clear the flags bit or point the event index at the next
> -	 * entry. Always do both to keep code simple. */
> -	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);
> -	}
> -	vring_used_event(&vq->vring) = cpu_to_virtio16(_vq->vdev, last_used_idx = vq->last_used_idx);
> -	END_USE(vq);
> -	return last_used_idx;
> +	return vq->packed ? virtqueue_enable_cb_prepare_packed(_vq) :
> +			    virtqueue_enable_cb_prepare_split(_vq);
>   }
>   EXPORT_SYMBOL_GPL(virtqueue_enable_cb_prepare);
>   
> +static bool virtqueue_poll_split(struct virtqueue *_vq, unsigned last_used_idx)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +
> +	virtio_mb(vq->weak_barriers);
> +	return (u16)last_used_idx != virtio16_to_cpu(_vq->vdev, vq->vring.used->idx);
> +}
> +
> +static bool virtqueue_poll_packed(struct virtqueue *_vq, unsigned last_used_idx)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	bool avail, used;
> +	u16 flags;
> +
> +	virtio_mb(vq->weak_barriers);
> +	flags = virtio16_to_cpu(vq->vq.vdev,
> +			vq->vring_packed.desc[last_used_idx].flags);
> +	avail = flags & VRING_DESC_F_AVAIL(1);
> +	used = flags & VRING_DESC_F_USED(1);
> +	return avail == used;
> +}
> +
>   /**
>    * virtqueue_poll - query pending used buffers
>    * @vq: the struct virtqueue we're talking about.
> @@ -829,8 +1379,8 @@ bool virtqueue_poll(struct virtqueue *_vq, unsigned last_used_idx)
>   {
>   	struct vring_virtqueue *vq = to_vvq(_vq);
>   
> -	virtio_mb(vq->weak_barriers);
> -	return (u16)last_used_idx != virtio16_to_cpu(_vq->vdev, vq->vring.used->idx);
> +	return vq->packed ? virtqueue_poll_packed(_vq, last_used_idx) :
> +			    virtqueue_poll_split(_vq, last_used_idx);
>   }
>   EXPORT_SYMBOL_GPL(virtqueue_poll);
>   
> @@ -852,6 +1402,83 @@ bool virtqueue_enable_cb(struct virtqueue *_vq)
>   }
>   EXPORT_SYMBOL_GPL(virtqueue_enable_cb);
>   
> +static bool virtqueue_enable_cb_delayed_split(struct virtqueue *_vq)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	u16 bufs;
> +
> +	START_USE(vq);
> +
> +	/* 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
> +	 * either clear the flags bit or point the event index at the next
> +	 * entry. Always update the event index to keep code simple. */
> +	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);
> +	}
> +	/* TODO: tune this threshold */
> +	bufs = (u16)(vq->avail_idx_shadow - vq->last_used_idx) * 3 / 4;
> +
> +	virtio_store_mb(vq->weak_barriers,
> +			&vring_used_event(&vq->vring),
> +			cpu_to_virtio16(_vq->vdev, vq->last_used_idx + bufs));
> +
> +	if (unlikely((u16)(virtio16_to_cpu(_vq->vdev, vq->vring.used->idx) - vq->last_used_idx) > bufs)) {
> +		END_USE(vq);
> +		return false;
> +	}
> +
> +	END_USE(vq);
> +	return true;
> +}
> +
> +static bool virtqueue_enable_cb_delayed_packed(struct virtqueue *_vq)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	u16 bufs, off_wrap, used_idx, wrap_counter;
> +
> +	START_USE(vq);
> +
> +	/* 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
> +	 * either clear the flags bit or point the event index at the next
> +	 * entry. Always update the event index to keep code simple. */
> +	if (vq->event_flags_shadow == VRING_EVENT_F_DISABLE) {
> +		vq->event_flags_shadow = vq->event ? VRING_EVENT_F_DESC:
> +						     VRING_EVENT_F_ENABLE;
> +		vq->vring_packed.driver->flags = cpu_to_virtio16(_vq->vdev,
> +							vq->event_flags_shadow);
> +	}
> +
> +	/* TODO: tune this threshold */
> +	bufs = (u16)(vq->next_avail_idx - vq->last_used_idx) * 3 / 4;
> +
> +	used_idx = vq->last_used_idx + bufs;
> +	if (used_idx >= vq->vring_packed.num)
> +		used_idx -= vq->vring_packed.num;
> +
> +	wrap_counter = vq->wrap_counter;
> +	if (used_idx > vq->next_avail_idx)
> +		wrap_counter ^= 1;
> +
> +	off_wrap = used_idx | (wrap_counter << 15);
> +
> +	virtio_store_mb(vq->weak_barriers, &vq->vring_packed.driver->off_wrap,
> +			cpu_to_virtio16(_vq->vdev, off_wrap));
> +
> +	if (more_used_packed(vq)) {
> +		END_USE(vq);
> +		return false;
> +	}
> +
> +	END_USE(vq);
> +	return true;
> +}
> +
>   /**
>    * virtqueue_enable_cb_delayed - restart callbacks after disable_cb.
>    * @vq: the struct virtqueue we're talking about.
> @@ -868,37 +1495,69 @@ EXPORT_SYMBOL_GPL(virtqueue_enable_cb);
>   bool virtqueue_enable_cb_delayed(struct virtqueue *_vq)
>   {
>   	struct vring_virtqueue *vq = to_vvq(_vq);
> -	u16 bufs;
>   
> -	START_USE(vq);
> -
> -	/* 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
> -	 * either clear the flags bit or point the event index at the next
> -	 * entry. Always update the event index to keep code simple. */
> -	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);
> -	}
> -	/* TODO: tune this threshold */
> -	bufs = (u16)(vq->avail_idx_shadow - vq->last_used_idx) * 3 / 4;
> -
> -	virtio_store_mb(vq->weak_barriers,
> -			&vring_used_event(&vq->vring),
> -			cpu_to_virtio16(_vq->vdev, vq->last_used_idx + bufs));
> -
> -	if (unlikely((u16)(virtio16_to_cpu(_vq->vdev, vq->vring.used->idx) - vq->last_used_idx) > bufs)) {
> -		END_USE(vq);
> -		return false;
> -	}
> -
> -	END_USE(vq);
> -	return true;
> +	return vq->packed ? virtqueue_enable_cb_delayed_packed(_vq) :
> +			    virtqueue_enable_cb_delayed_split(_vq);
>   }
>   EXPORT_SYMBOL_GPL(virtqueue_enable_cb_delayed);
>   
> +static void *virtqueue_detach_unused_buf_split(struct virtqueue *_vq)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	unsigned int i;
> +	void *buf;
> +
> +	START_USE(vq);
> +
> +	for (i = 0; i < vq->vring.num; i++) {
> +		if (!vq->desc_state[i].data)
> +			continue;
> +		/* detach_buf clears data, so grab it now. */
> +		buf = vq->desc_state[i].data;
> +		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);
> +
> +	END_USE(vq);
> +	return NULL;
> +}
> +
> +static void *virtqueue_detach_unused_buf_packed(struct virtqueue *_vq)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	unsigned int i, num;
> +	void *buf;
> +
> +	START_USE(vq);
> +
> +	for (i = 0; i < vq->vring_packed.num; i++) {
> +		if (!vq->desc_state[i].data)
> +			continue;
> +		/* detach_buf clears data, so grab it now. */
> +		buf = vq->desc_state[i].data;
> +		num = detach_buf_packed(vq, i, NULL);
> +		if (vq->next_avail_idx < num) {
> +			vq->next_avail_idx = vq->vring_packed.num -
> +					(num - vq->next_avail_idx);
> +			vq->wrap_counter ^= 1;
> +		} else {
> +			vq->next_avail_idx -= num;
> +		}
> +		END_USE(vq);
> +		return buf;
> +	}
> +	/* That should have freed everything. */
> +	BUG_ON(vq->vq.num_free != vq->vring_packed.num);
> +
> +	END_USE(vq);
> +	return NULL;
> +}
> +
>   /**
>    * virtqueue_detach_unused_buf - detach first unused buffer
>    * @vq: the struct virtqueue we're talking about.
> @@ -910,27 +1569,9 @@ EXPORT_SYMBOL_GPL(virtqueue_enable_cb_delayed);
>   void *virtqueue_detach_unused_buf(struct virtqueue *_vq)
>   {
>   	struct vring_virtqueue *vq = to_vvq(_vq);
> -	unsigned int i;
> -	void *buf;
>   
> -	START_USE(vq);
> -
> -	for (i = 0; i < vq->vring.num; i++) {
> -		if (!vq->desc_state[i].data)
> -			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);
> -		END_USE(vq);
> -		return buf;
> -	}
> -	/* That should have freed everything. */
> -	BUG_ON(vq->vq.num_free != vq->vring.num);
> -
> -	END_USE(vq);
> -	return NULL;
> +	return vq->packed ? virtqueue_detach_unused_buf_packed(_vq) :
> +			    virtqueue_detach_unused_buf_split(_vq);
>   }
>   EXPORT_SYMBOL_GPL(virtqueue_detach_unused_buf);
>   
> @@ -955,7 +1596,8 @@ 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,
> @@ -963,19 +1605,20 @@ 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;
> @@ -984,9 +1627,8 @@ 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;
> @@ -997,18 +1639,37 @@ 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->next_avail_idx = 0;
> +		vq->wrap_counter = 1;
> +		vq->event_flags_shadow = 0;
> +	} 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) {
> +			vq->event_flags_shadow = VRING_EVENT_F_DISABLE;
> +			vq->vring_packed.driver->flags = cpu_to_virtio16(vdev,
> +						vq->event_flags_shadow);
> +		} 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;
>   }
> @@ -1056,6 +1717,22 @@ 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)
> +{
> +	return packed ? vring_packed_size(num, align) : vring_size(num, align);
> +}
> +
> +static inline void vring_packed_init(struct vring_packed *vr, unsigned int num,
> +				     void *p, unsigned long align)
> +{
> +	vr->num = num;
> +	vr->desc = p;
> +	vr->driver = (void *)(((uintptr_t)p + sizeof(struct vring_packed_desc)
> +		* num + align - 1) & ~(align - 1));
> +	vr->device = vr->driver + 1;
> +}
> +
>   struct virtqueue *vring_create_virtqueue(
>   	unsigned int index,
>   	unsigned int num,
> @@ -1072,7 +1749,8 @@ 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)) {
> @@ -1080,9 +1758,13 @@ 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)
> @@ -1094,17 +1776,21 @@ 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);
> @@ -1130,10 +1816,17 @@ 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);
>   
> @@ -1143,7 +1836,9 @@ 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);
> @@ -1157,14 +1852,18 @@ void vring_transport_features(struct virtio_device *vdev)
>   
>   	for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++) {
>   		switch (i) {
> -		case VIRTIO_RING_F_INDIRECT_DESC:
> +#if 0
> +		case VIRTIO_RING_F_INDIRECT_DESC: // FIXME not tested yet.
>   			break;
> -		case VIRTIO_RING_F_EVENT_IDX:
> +		case VIRTIO_RING_F_EVENT_IDX: // FIXME probably not work.
>   			break;
> +#endif
>   		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);
> @@ -1185,7 +1884,7 @@ 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);
>   
> @@ -1228,6 +1927,10 @@ dma_addr_t virtqueue_get_avail_addr(struct virtqueue *_vq)
>   
>   	BUG_ON(!vq->we_own_ring);
>   
> +	if (vq->packed)
> +		return vq->queue_dma_addr + ((char *)vq->vring_packed.driver -
> +				(char *)vq->vring_packed.desc);
> +
>   	return vq->queue_dma_addr +
>   		((char *)vq->vring.avail - (char *)vq->vring.desc);
>   }
> @@ -1239,11 +1942,16 @@ dma_addr_t virtqueue_get_used_addr(struct virtqueue *_vq)
>   
>   	BUG_ON(!vq->we_own_ring);
>   
> +	if (vq->packed)
> +		return vq->queue_dma_addr + ((char *)vq->vring_packed.device -
> +				(char *)vq->vring_packed.desc);
> +
>   	return vq->queue_dma_addr +
>   		((char *)vq->vring.used - (char *)vq->vring.desc);
>   }
>   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,
> diff --git a/include/uapi/linux/virtio_config.h b/include/uapi/linux/virtio_config.h
> index 308e2096291f..a6e392325e3a 100644
> --- a/include/uapi/linux/virtio_config.h
> +++ b/include/uapi/linux/virtio_config.h
> @@ -49,7 +49,7 @@
>    * transport being used (eg. virtio_ring), the rest are per-device feature
>    * bits. */
>   #define VIRTIO_TRANSPORT_F_START	28
> -#define VIRTIO_TRANSPORT_F_END		34
> +#define VIRTIO_TRANSPORT_F_END		36
>   
>   #ifndef VIRTIO_CONFIG_NO_LEGACY
>   /* Do we get callbacks when the ring is completely used, even if we've
> @@ -71,4 +71,14 @@
>    * this is for compatibility with legacy systems.
>    */
>   #define VIRTIO_F_IOMMU_PLATFORM		33
> +
> +/* This feature indicates support for the packed virtqueue layout. */
> +#define VIRTIO_F_RING_PACKED		34
> +
> +/*
> + * This feature indicates that all buffers are used by the device
> + * in the same order in which they have been made available.
> + */
> +#define VIRTIO_F_IN_ORDER		35
> +
>   #endif /* _UAPI_LINUX_VIRTIO_CONFIG_H */
> diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h
> index 6d5d5faa989b..735d4207c988 100644
> --- a/include/uapi/linux/virtio_ring.h
> +++ b/include/uapi/linux/virtio_ring.h
> @@ -44,6 +44,9 @@
>   /* This means the buffer contains a list of buffer descriptors. */
>   #define VRING_DESC_F_INDIRECT	4
>   
> +#define VRING_DESC_F_AVAIL(b)	((b) << 7)
> +#define VRING_DESC_F_USED(b)	((b) << 15)
> +
>   /* The Host uses this in used->flags to advise the Guest: don't kick me when
>    * you add a buffer.  It's unreliable, so it's simply an optimization.  Guest
>    * will still kick if it's out of buffers. */
> @@ -53,6 +56,10 @@
>    * optimization.  */
>   #define VRING_AVAIL_F_NO_INTERRUPT	1
>   
> +#define VRING_EVENT_F_ENABLE	0x0
> +#define VRING_EVENT_F_DISABLE	0x1
> +#define VRING_EVENT_F_DESC	0x2
> +
>   /* We support indirect buffer descriptors */
>   #define VIRTIO_RING_F_INDIRECT_DESC	28
>   
> @@ -171,4 +178,58 @@ static inline int vring_need_event(__u16 event_idx, __u16 new_idx, __u16 old)
>   	return (__u16)(new_idx - event_idx - 1) < (__u16)(new_idx - old);
>   }
>   
> +struct vring_packed_desc_event {
> +	/* __virtio16 off  : 15; // Descriptor Event Offset
> +	 * __virtio16 wrap : 1;  // Descriptor Event Wrap Counter */
> +	__virtio16 off_wrap;
> +	/* __virtio16 flags : 2; // Descriptor Event Flags */
> +	__virtio16 flags;
> +};
> +
> +struct vring_packed_desc {
> +	/* Buffer Address. */
> +	__virtio64 addr;
> +	/* Buffer Length. */
> +	__virtio32 len;
> +	/* Buffer ID. */
> +	__virtio16 id;
> +	/* The flags depending on descriptor type. */
> +	__virtio16 flags;
> +};
> +
> +struct vring_packed {
> +	unsigned int num;
> +
> +	struct vring_packed_desc *desc;
> +
> +	struct vring_packed_desc_event *driver;
> +
> +	struct vring_packed_desc_event *device;
> +};
> +
> +/* The standard layout for the packed ring is a continuous chunk of memory
> + * which looks like this.
> + *
> + * struct vring_packed
> + * {
> + *	// The actual descriptors (16 bytes each)
> + *	struct vring_packed_desc desc[num];
> + *
> + *	// Padding to the next align boundary.
> + *	char pad[];
> + *
> + *	// Driver Event Suppression
> + *	struct vring_packed_desc_event driver;
> + *
> + *	// Device Event Suppression
> + *	struct vring_packed_desc_event device;
> + * };
> + */
> +
> +static inline unsigned vring_packed_size(unsigned int num, unsigned long align)
> +{
> +	return ((sizeof(struct vring_packed_desc) * num + align - 1)
> +		& ~(align - 1)) + sizeof(struct vring_packed_desc_event) * 2;
> +}
> +
>   #endif /* _UAPI_LINUX_VIRTIO_RING_H */