[mirror_ubuntu-bionic-kernel.git] / drivers / virtio / virtio_ring.c

/* Virtio ring implementation.
 *
 *  Copyright 2007 Rusty Russell IBM Corporation
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
#include <linux/virtio.h>
#include <linux/virtio_ring.h>
#include <linux/virtio_config.h>
#include <linux/device.h>
#include <linux/slab.h>
#include <linux/module.h>
#include <linux/hrtimer.h>
#include <linux/kmemleak.h>
#include <linux/dma-mapping.h>
#include <xen/xen.h>

#ifdef DEBUG
/* For development, we want to crash whenever the ring is screwed. */
#define BAD_RING(_vq, fmt, args...)                             \
        do {                                                    \
                dev_err(&(_vq)->vq.vdev->dev,                   \
                        "%s:"fmt, (_vq)->vq.name, ##args);      \
                BUG();                                          \
        } while (0)
/* Caller is supposed to guarantee no reentry. */
#define START_USE(_vq)                                          \
        do {                                                    \
                if ((_vq)->in_use)                              \
                        panic("%s:in_use = %i\n",               \
                              (_vq)->vq.name, (_vq)->in_use);   \
                (_vq)->in_use = __LINE__;                       \
        } while (0)
#define END_USE(_vq) \
        do { BUG_ON(!(_vq)->in_use); (_vq)->in_use = 0; } while(0)
#else
#define BAD_RING(_vq, fmt, args...)                             \
        do {                                                    \
                dev_err(&_vq->vq.vdev->dev,                     \
                        "%s:"fmt, (_vq)->vq.name, ##args);      \
                (_vq)->broken = true;                           \
        } while (0)
#define START_USE(vq)
#define END_USE(vq)
#endif

struct vring_desc_state {
        void *data;                     /* Data for callback. */
        struct vring_desc *indir_desc;  /* Indirect descriptor, if any. */
};

struct vring_virtqueue {
        struct virtqueue vq;

        /* Actual memory layout for this queue */
        struct vring vring;

        /* Can we use weak barriers? */
        bool weak_barriers;

        /* Other side has made a mess, don't try any more. */
        bool broken;

        /* Host supports indirect buffers */
        bool indirect;

        /* 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;

        /* Last written value to avail->idx in guest byte order */
        u16 avail_idx_shadow;

        /* How to notify other side. FIXME: commonalize hcalls! */
        bool (*notify)(struct virtqueue *vq);

        /* DMA, allocation, and size information */
        bool we_own_ring;
        size_t queue_size_in_bytes;
        dma_addr_t queue_dma_addr;

#ifdef DEBUG
        /* They're supposed to lock for us. */
        unsigned int in_use;

        /* Figure out if their kicks are too delayed. */
        bool last_add_time_valid;
        ktime_t last_add_time;
#endif

        /* Per-descriptor state. */
        struct vring_desc_state desc_state[];
};

#define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)

/*
 * Modern virtio devices have feature bits to specify whether they need a
 * quirk and bypass the IOMMU. If not there, just use the DMA API.
 *
 * If there, the interaction between virtio and DMA API is messy.
 *
 * On most systems with virtio, physical addresses match bus addresses,
 * and it doesn't particularly matter whether we use the DMA API.
 *
 * On some systems, including Xen and any system with a physical device
 * that speaks virtio behind a physical IOMMU, we must use the DMA API
 * for virtio DMA to work at all.
 *
 * On other systems, including SPARC and PPC64, virtio-pci devices are
 * enumerated as though they are behind an IOMMU, but the virtio host
 * ignores the IOMMU, so we must either pretend that the IOMMU isn't
 * there or somehow map everything as the identity.
 *
 * For the time being, we preserve historic behavior and bypass the DMA
 * API.
 *
 * TODO: install a per-device DMA ops structure that does the right thing
 * taking into account all the above quirks, and use the DMA API
 * unconditionally on data path.
 */

static bool vring_use_dma_api(struct virtio_device *vdev)
{
        if (!virtio_has_iommu_quirk(vdev))
                return true;

        /* Otherwise, we are left to guess. */
        /*
         * In theory, it's possible to have a buggy QEMU-supposed
         * emulated Q35 IOMMU and Xen enabled at the same time.  On
         * such a configuration, virtio has never worked and will
         * not work without an even larger kludge.  Instead, enable
         * the DMA API if we're a Xen guest, which at least allows
         * all of the sensible Xen configurations to work correctly.
         */
        if (xen_domain())
                return true;

        return false;
}

/*
 * The DMA ops on various arches are rather gnarly right now, and
 * making all of the arch DMA ops work on the vring device itself
 * is a mess.  For now, we use the parent device for DMA ops.
 */
static inline struct device *vring_dma_dev(const struct vring_virtqueue *vq)
{
        return vq->vq.vdev->dev.parent;
}

/* Map one sg entry. */
static dma_addr_t vring_map_one_sg(const struct vring_virtqueue *vq,
                                   struct scatterlist *sg,
                                   enum dma_data_direction direction)
{
        if (!vring_use_dma_api(vq->vq.vdev))
                return (dma_addr_t)sg_phys(sg);

        /*
         * We can't use dma_map_sg, because we don't use scatterlists in
         * the way it expects (we don't guarantee that the scatterlist
         * will exist for the lifetime of the mapping).
         */
        return dma_map_page(vring_dma_dev(vq),
                            sg_page(sg), sg->offset, sg->length,
                            direction);
}

static dma_addr_t vring_map_single(const struct vring_virtqueue *vq,
                                   void *cpu_addr, size_t size,
                                   enum dma_data_direction direction)
{
        if (!vring_use_dma_api(vq->vq.vdev))
                return (dma_addr_t)virt_to_phys(cpu_addr);

        return dma_map_single(vring_dma_dev(vq),
                              cpu_addr, size, direction);
}

static void vring_unmap_one(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 int vring_mapping_error(const struct vring_virtqueue *vq,
                               dma_addr_t addr)
{
        if (!vring_use_dma_api(vq->vq.vdev))
                return 0;

        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)
{
        struct vring_desc *desc;
        unsigned int i;

        /*
         * 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_desc), gfp);
        if (!desc)
                return NULL;

        for (i = 0; i < total_sg; i++)
                desc[i].next = cpu_to_virtio16(_vq->vdev, i + 1);
        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)
{
        struct vring_virtqueue *vq = to_vvq(_vq);
        struct scatterlist *sg;
        struct vring_desc *desc;
        unsigned int i, n, avail, descs_used, uninitialized_var(prev), err_idx;
        int head;
        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 > vq->vring.num);
        BUG_ON(total_sg == 0);

        head = vq->free_head;

        /* 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);
        else
                desc = NULL;

        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.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; 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;

                        desc[i].flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_NEXT);
                        desc[i].addr = cpu_to_virtio64(_vq->vdev, addr);
                        desc[i].len = cpu_to_virtio32(_vq->vdev, sg->length);
                        prev = i;
                        i = virtio16_to_cpu(_vq->vdev, desc[i].next);
                }
        }
        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;

                        desc[i].flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_NEXT | VRING_DESC_F_WRITE);
                        desc[i].addr = cpu_to_virtio64(_vq->vdev, addr);
                        desc[i].len = cpu_to_virtio32(_vq->vdev, sg->length);
                        prev = i;
                        i = virtio16_to_cpu(_vq->vdev, desc[i].next);
                }
        }
        /* Last one doesn't continue. */
        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_desc),
                        DMA_TO_DEVICE);
                if (vring_mapping_error(vq, addr))
                        goto unmap_release;

                vq->vring.desc[head].flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_INDIRECT);
                vq->vring.desc[head].addr = cpu_to_virtio64(_vq->vdev, addr);

                vq->vring.desc[head].len = cpu_to_virtio32(_vq->vdev, total_sg * sizeof(struct vring_desc));
        }

        /* We're using some buffers from the free list. */
        vq->vq.num_free -= descs_used;

        /* Update free pointer */
        if (indirect)
                vq->free_head = virtio16_to_cpu(_vq->vdev, vq->vring.desc[head].next);
        else
                vq->free_head = i;

        /* Store token and indirect buffer state. */
        vq->desc_state[head].data = data;
        if (indirect)
                vq->desc_state[head].indir_desc = desc;
        if (ctx)
                vq->desc_state[head].indir_desc = ctx;

        /* Put entry in available array (but don't update avail->idx until they
         * do sync). */
        avail = vq->avail_idx_shadow & (vq->vring.num - 1);
        vq->vring.avail->ring[avail] = cpu_to_virtio16(_vq->vdev, head);

        /* Descriptors and available array need to be set before we expose the
         * new available array entries. */
        virtio_wmb(vq->weak_barriers);
        vq->avail_idx_shadow++;
        vq->vring.avail->idx = cpu_to_virtio16(_vq->vdev, vq->avail_idx_shadow);
        vq->num_added++;

        pr_debug("Added buffer head %i to %p\n", head, vq);
        END_USE(vq);

        /* This is very unlikely, but theoretically possible.  Kick
         * just in case. */
        if (unlikely(vq->num_added == (1 << 16) - 1))
                virtqueue_kick(_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 = virtio16_to_cpu(_vq->vdev, vq->vring.desc[i].next);
        }

        vq->vq.num_free += total_sg;

        if (indirect)
                kfree(desc);

        END_USE(vq);
        return -EIO;
}

/**
 * virtqueue_add_sgs - expose buffers to other end
 * @vq: the struct virtqueue we're talking about.
 * @sgs: array of terminated scatterlists.
 * @out_num: the number of scatterlists readable by other side
 * @in_num: the number of scatterlists which are writable (after readable ones)
 * @data: the token identifying the buffer.
 * @gfp: how to do memory allocations (if necessary).
 *
 * Caller must ensure we don't call this with other virtqueue operations
 * at the same time (except where noted).
 *
 * Returns zero or a negative error (ie. ENOSPC, ENOMEM, EIO).
 */
int virtqueue_add_sgs(struct virtqueue *_vq,
                      struct scatterlist *sgs[],
                      unsigned int out_sgs,
                      unsigned int in_sgs,
                      void *data,
                      gfp_t gfp)
{
        unsigned int i, total_sg = 0;

        /* Count them first. */
        for (i = 0; i < out_sgs + in_sgs; i++) {
                struct scatterlist *sg;
                for (sg = sgs[i]; sg; sg = sg_next(sg))
                        total_sg++;
        }
        return virtqueue_add(_vq, sgs, total_sg, out_sgs, in_sgs,
                             data, NULL, gfp);
}
EXPORT_SYMBOL_GPL(virtqueue_add_sgs);

/**
 * virtqueue_add_outbuf - expose output buffers to other end
 * @vq: the struct virtqueue we're talking about.
 * @sg: scatterlist (must be well-formed and terminated!)
 * @num: the number of entries in @sg readable by other side
 * @data: the token identifying the buffer.
 * @gfp: how to do memory allocations (if necessary).
 *
 * Caller must ensure we don't call this with other virtqueue operations
 * at the same time (except where noted).
 *
 * Returns zero or a negative error (ie. ENOSPC, ENOMEM, EIO).
 */
int virtqueue_add_outbuf(struct virtqueue *vq,
                         struct scatterlist *sg, unsigned int num,
                         void *data,
                         gfp_t gfp)
{
        return virtqueue_add(vq, &sg, num, 1, 0, data, NULL, gfp);
}
EXPORT_SYMBOL_GPL(virtqueue_add_outbuf);

/**
 * virtqueue_add_inbuf - expose input buffers to other end
 * @vq: the struct virtqueue we're talking about.
 * @sg: scatterlist (must be well-formed and terminated!)
 * @num: the number of entries in @sg writable by other side
 * @data: the token identifying the buffer.
 * @gfp: how to do memory allocations (if necessary).
 *
 * Caller must ensure we don't call this with other virtqueue operations
 * at the same time (except where noted).
 *
 * Returns zero or a negative error (ie. ENOSPC, ENOMEM, EIO).
 */
int virtqueue_add_inbuf(struct virtqueue *vq,
                        struct scatterlist *sg, unsigned int num,
                        void *data,
                        gfp_t gfp)
{
        return virtqueue_add(vq, &sg, num, 0, 1, data, NULL, gfp);
}
EXPORT_SYMBOL_GPL(virtqueue_add_inbuf);

/**
 * virtqueue_add_inbuf_ctx - expose input buffers to other end
 * @vq: the struct virtqueue we're talking about.
 * @sg: scatterlist (must be well-formed and terminated!)
 * @num: the number of entries in @sg writable by other side
 * @data: the token identifying the buffer.
 * @ctx: extra context for the token
 * @gfp: how to do memory allocations (if necessary).
 *
 * Caller must ensure we don't call this with other virtqueue operations
 * at the same time (except where noted).
 *
 * Returns zero or a negative error (ie. ENOSPC, ENOMEM, EIO).
 */
int virtqueue_add_inbuf_ctx(struct virtqueue *vq,
                        struct scatterlist *sg, unsigned int num,
                        void *data,
                        void *ctx,
                        gfp_t gfp)
{
        return virtqueue_add(vq, &sg, num, 0, 1, data, ctx, gfp);
}
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)
{
        struct vring_virtqueue *vq = to_vvq(_vq);
        u16 new, old;
        bool needs_kick;

        START_USE(vq);
        /* We need to expose available array entries before checking avail
         * event. */
        virtio_mb(vq->weak_barriers);

        old = vq->avail_idx_shadow - vq->num_added;
        new = vq->avail_idx_shadow;
        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

        if (vq->event) {
                needs_kick = vring_need_event(virtio16_to_cpu(_vq->vdev, vring_avail_event(&vq->vring)),
                                              new, old);
        } else {
                needs_kick = !(vq->vring.used->flags & cpu_to_virtio16(_vq->vdev, VRING_USED_F_NO_NOTIFY));
        }
        END_USE(vq);
        return needs_kick;
}
EXPORT_SYMBOL_GPL(virtqueue_kick_prepare);

/**
 * virtqueue_notify - second half of split virtqueue_kick call.
 * @vq: the struct virtqueue
 *
 * This does not need to be serialized.
 *
 * Returns false if host notify failed or queue is broken, otherwise true.
 */
bool virtqueue_notify(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        if (unlikely(vq->broken))
                return false;

        /* Prod other side to tell it about changes. */
        if (!vq->notify(_vq)) {
                vq->broken = true;
                return false;
        }
        return true;
}
EXPORT_SYMBOL_GPL(virtqueue_notify);

/**
 * virtqueue_kick - update after add_buf
 * @vq: the struct virtqueue
 *
 * After one or more virtqueue_add_* calls, invoke this to kick
 * the other side.
 *
 * Caller must ensure we don't call this with other virtqueue
 * operations at the same time (except where noted).
 *
 * Returns false if kick failed, otherwise true.
 */
bool virtqueue_kick(struct virtqueue *vq)
{
        if (virtqueue_kick_prepare(vq))
                return virtqueue_notify(vq);
        return true;
}
EXPORT_SYMBOL_GPL(virtqueue_kick);

static void detach_buf(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);

        /* Clear data ptr. */
        vq->desc_state[head].data = NULL;

        /* Put back on free list: unmap first-level descriptors and find end */
        i = head;

        while (vq->vring.desc[i].flags & nextflag) {
                vring_unmap_one(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]);
        vq->vring.desc[i].next = cpu_to_virtio16(vq->vq.vdev, vq->free_head);
        vq->free_head = head;

        /* Plus final descriptor */
        vq->vq.num_free++;

        if (vq->indirect) {
                struct vring_desc *indir_desc = vq->desc_state[head].indir_desc;
                u32 len;

                /* Free the indirect table, if any, now that it's unmapped. */
                if (!indir_desc)
                        return;

                len = virtio32_to_cpu(vq->vq.vdev, vq->vring.desc[head].len);

                BUG_ON(!(vq->vring.desc[head].flags &
                         cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_INDIRECT)));
                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]);

                kfree(indir_desc);
                vq->desc_state[head].indir_desc = NULL;
        } else if (ctx) {
                *ctx = vq->desc_state[head].indir_desc;
        }
}

static inline bool more_used(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)
{
        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;
}
EXPORT_SYMBOL_GPL(virtqueue_get_buf_ctx);

void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len)
{
        return virtqueue_get_buf_ctx(_vq, len, NULL);
}
EXPORT_SYMBOL_GPL(virtqueue_get_buf);
/**
 * virtqueue_disable_cb - disable callbacks
 * @vq: the struct virtqueue we're talking about.
 *
 * Note that this is not necessarily synchronous, hence unreliable and only
 * useful as an optimization.
 *
 * Unlike other operations, this need not be serialized.
 */
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);
        }

}
EXPORT_SYMBOL_GPL(virtqueue_disable_cb);

/**
 * virtqueue_enable_cb_prepare - restart callbacks after disable_cb
 * @vq: the struct virtqueue we're talking about.
 *
 * This re-enables callbacks; it returns current queue state
 * in an opaque unsigned value. This value should be later tested by
 * virtqueue_poll, to detect a possible race between the driver checking for
 * more work, and enabling callbacks.
 *
 * Caller must ensure we don't call this with other virtqueue
 * operations at the same time (except where noted).
 */
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;
}
EXPORT_SYMBOL_GPL(virtqueue_enable_cb_prepare);

/**
 * virtqueue_poll - query pending used buffers
 * @vq: the struct virtqueue we're talking about.
 * @last_used_idx: virtqueue state (from call to virtqueue_enable_cb_prepare).
 *
 * Returns "true" if there are pending used buffers in the queue.
 *
 * This does not need to be serialized.
 */
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);
}
EXPORT_SYMBOL_GPL(virtqueue_poll);

/**
 * virtqueue_enable_cb - restart callbacks after disable_cb.
 * @vq: the struct virtqueue we're talking about.
 *
 * This re-enables callbacks; it returns "false" if there are pending
 * buffers in the queue, to detect a possible race between the driver
 * checking for more work, and enabling callbacks.
 *
 * Caller must ensure we don't call this with other virtqueue
 * operations at the same time (except where noted).
 */
bool virtqueue_enable_cb(struct virtqueue *_vq)
{
        unsigned last_used_idx = virtqueue_enable_cb_prepare(_vq);
        return !virtqueue_poll(_vq, last_used_idx);
}
EXPORT_SYMBOL_GPL(virtqueue_enable_cb);

/**
 * virtqueue_enable_cb_delayed - restart callbacks after disable_cb.
 * @vq: the struct virtqueue we're talking about.
 *
 * This re-enables callbacks but hints to the other side to delay
 * interrupts until most of the available buffers have been processed;
 * it returns "false" if there are many pending buffers in the queue,
 * to detect a possible race between the driver checking for more work,
 * and enabling callbacks.
 *
 * Caller must ensure we don't call this with other virtqueue
 * operations at the same time (except where noted).
 */
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;
}
EXPORT_SYMBOL_GPL(virtqueue_enable_cb_delayed);

/**
 * virtqueue_detach_unused_buf - detach first unused buffer
 * @vq: the struct virtqueue we're talking about.
 *
 * Returns NULL or the "data" token handed to virtqueue_add_*().
 * This is not valid on an active queue; it is useful only for device
 * shutdown.
 */
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;
}
EXPORT_SYMBOL_GPL(virtqueue_detach_unused_buf);

irqreturn_t vring_interrupt(int irq, void *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        if (!more_used(vq)) {
                pr_debug("virtqueue interrupt with no work for %p\n", vq);
                return IRQ_NONE;
        }

        if (unlikely(vq->broken))
                return IRQ_HANDLED;

        pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback);
        if (vq->vq.callback)
                vq->vq.callback(&vq->vq);

        return IRQ_HANDLED;
}
EXPORT_SYMBOL_GPL(vring_interrupt);

struct virtqueue *__vring_new_virtqueue(unsigned int index,
                                        struct vring vring,
                                        struct virtio_device *vdev,
                                        bool weak_barriers,
                                        bool context,
                                        bool (*notify)(struct virtqueue *),
                                        void (*callback)(struct virtqueue *),
                                        const char *name)
{
        unsigned int i;
        struct vring_virtqueue *vq;

        vq = kmalloc(sizeof(*vq) + vring.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.index = index;
        vq->we_own_ring = false;
        vq->queue_dma_addr = 0;
        vq->queue_size_in_bytes = 0;
        vq->notify = notify;
        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;
        list_add_tail(&vq->vq.list, &vdev->vqs);
#ifdef DEBUG
        vq->in_use = false;
        vq->last_add_time_valid = false;
#endif

        vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC) &&
                !context;
        vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);

        /* 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);
        }

        /* 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));

        return &vq->vq;
}
EXPORT_SYMBOL_GPL(__vring_new_virtqueue);

static void *vring_alloc_queue(struct virtio_device *vdev, size_t size,
                              dma_addr_t *dma_handle, gfp_t flag)
{
        if (vring_use_dma_api(vdev)) {
                return dma_alloc_coherent(vdev->dev.parent, size,
                                          dma_handle, flag);
        } else {
                void *queue = alloc_pages_exact(PAGE_ALIGN(size), flag);
                if (queue) {
                        phys_addr_t phys_addr = virt_to_phys(queue);
                        *dma_handle = (dma_addr_t)phys_addr;

                        /*
                         * Sanity check: make sure we dind't truncate
                         * the address.  The only arches I can find that
                         * have 64-bit phys_addr_t but 32-bit dma_addr_t
                         * are certain non-highmem MIPS and x86
                         * configurations, but these configurations
                         * should never allocate physical pages above 32
                         * bits, so this is fine.  Just in case, throw a
                         * warning and abort if we end up with an
                         * unrepresentable address.
                         */
                        if (WARN_ON_ONCE(*dma_handle != phys_addr)) {
                                free_pages_exact(queue, PAGE_ALIGN(size));
                                return NULL;
                        }
                }
                return queue;
        }
}

static void vring_free_queue(struct virtio_device *vdev, size_t size,
                             void *queue, dma_addr_t dma_handle)
{
        if (vring_use_dma_api(vdev)) {
                dma_free_coherent(vdev->dev.parent, size, queue, dma_handle);
        } else {
                free_pages_exact(queue, PAGE_ALIGN(size));
        }
}

struct virtqueue *vring_create_virtqueue(
        unsigned int index,
        unsigned int num,
        unsigned int vring_align,
        struct virtio_device *vdev,
        bool weak_barriers,
        bool may_reduce_num,
        bool context,
        bool (*notify)(struct virtqueue *),
        void (*callback)(struct virtqueue *),
        const char *name)
{
        struct virtqueue *vq;
        void *queue = NULL;
        dma_addr_t dma_addr;
        size_t queue_size_in_bytes;
        struct vring vring;

        /* We assume num is a power of 2. */
        if (num & (num - 1)) {
                dev_warn(&vdev->dev, "Bad virtqueue length %u\n", num);
                return NULL;
        }

        /* 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),
                                          &dma_addr,
                                          GFP_KERNEL|__GFP_NOWARN|__GFP_ZERO);
                if (queue)
                        break;
        }

        if (!num)
                return NULL;

        if (!queue) {
                /* Try to get a single page. You are my only hope! */
                queue = vring_alloc_queue(vdev, vring_size(num, vring_align),
                                          &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);

        vq = __vring_new_virtqueue(index, vring, vdev, weak_barriers, context,
                                   notify, callback, name);
        if (!vq) {
                vring_free_queue(vdev, queue_size_in_bytes, queue,
                                 dma_addr);
                return NULL;
        }

        to_vvq(vq)->queue_dma_addr = dma_addr;
        to_vvq(vq)->queue_size_in_bytes = queue_size_in_bytes;
        to_vvq(vq)->we_own_ring = true;

        return vq;
}
EXPORT_SYMBOL_GPL(vring_create_virtqueue);

struct virtqueue *vring_new_virtqueue(unsigned int index,
                                      unsigned int num,
                                      unsigned int vring_align,
                                      struct virtio_device *vdev,
                                      bool weak_barriers,
                                      bool context,
                                      void *pages,
                                      bool (*notify)(struct virtqueue *vq),
                                      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);
}
EXPORT_SYMBOL_GPL(vring_new_virtqueue);

void vring_del_virtqueue(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        if (vq->we_own_ring) {
                vring_free_queue(vq->vq.vdev, vq->queue_size_in_bytes,
                                 vq->vring.desc, vq->queue_dma_addr);
        }
        list_del(&_vq->list);
        kfree(vq);
}
EXPORT_SYMBOL_GPL(vring_del_virtqueue);

/* Manipulates transport-specific feature bits. */
void vring_transport_features(struct virtio_device *vdev)
{
        unsigned int i;

        for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++) {
                switch (i) {
                case VIRTIO_RING_F_INDIRECT_DESC:
                        break;
                case VIRTIO_RING_F_EVENT_IDX:
                        break;
                case VIRTIO_F_VERSION_1:
                        break;
                case VIRTIO_F_IOMMU_PLATFORM:
                        break;
                default:
                        /* We don't understand this bit. */
                        __virtio_clear_bit(vdev, i);
                }
        }
}
EXPORT_SYMBOL_GPL(vring_transport_features);

/**
 * virtqueue_get_vring_size - return the size of the virtqueue's vring
 * @vq: the struct virtqueue containing the vring of interest.
 *
 * Returns the size of the vring.  This is mainly used for boasting to
 * userspace.  Unlike other operations, this need not be serialized.
 */
unsigned int virtqueue_get_vring_size(struct virtqueue *_vq)
{

        struct vring_virtqueue *vq = to_vvq(_vq);

        return vq->vring.num;
}
EXPORT_SYMBOL_GPL(virtqueue_get_vring_size);

bool virtqueue_is_broken(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        return vq->broken;
}
EXPORT_SYMBOL_GPL(virtqueue_is_broken);

/*
 * This should prevent the device from being used, allowing drivers to
 * recover.  You may need to grab appropriate locks to flush.
 */
void virtio_break_device(struct virtio_device *dev)
{
        struct virtqueue *_vq;

        list_for_each_entry(_vq, &dev->vqs, list) {
                struct vring_virtqueue *vq = to_vvq(_vq);
                vq->broken = true;
        }
}
EXPORT_SYMBOL_GPL(virtio_break_device);

dma_addr_t virtqueue_get_desc_addr(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        BUG_ON(!vq->we_own_ring);

        return vq->queue_dma_addr;
}
EXPORT_SYMBOL_GPL(virtqueue_get_desc_addr);

dma_addr_t virtqueue_get_avail_addr(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        BUG_ON(!vq->we_own_ring);

        return vq->queue_dma_addr +
                ((char *)vq->vring.avail - (char *)vq->vring.desc);
}
EXPORT_SYMBOL_GPL(virtqueue_get_avail_addr);

dma_addr_t virtqueue_get_used_addr(struct virtqueue *_vq)
{
        struct vring_virtqueue *vq = to_vvq(_vq);

        BUG_ON(!vq->we_own_ring);

        return vq->queue_dma_addr +
                ((char *)vq->vring.used - (char *)vq->vring.desc);
}
EXPORT_SYMBOL_GPL(virtqueue_get_used_addr);

const struct vring *virtqueue_get_vring(struct virtqueue *vq)
{
        return &to_vvq(vq)->vring;
}
EXPORT_SYMBOL_GPL(virtqueue_get_vring);

MODULE_LICENSE("GPL");