virtio: Add improved queue allocation API

This leaves vring_new_virtqueue alone for compatbility, but it
adds two new improved APIs:

vring_create_virtqueue: Creates a virtqueue backed by automatically
allocated coherent memory.  (Some day it this could be extended to
support non-coherent memory, too, if there ends up being a platform
on which it's worthwhile.)

__vring_new_virtqueue: Creates a virtqueue with a manually-specified
layout.  This should allow mic_virtio to work much more cleanly.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

3 files changed, 235 insertions, 32 deletions

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 9abc008ff7ea..e46d08107a50 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -95,6 +95,11 @@ struct vring_virtqueue {
         /* 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;
@@ -878,36 +883,31 @@ irqreturn_t vring_interrupt(int irq, void *_vq)
 }
 EXPORT_SYMBOL_GPL(vring_interrupt);
 
-struct virtqueue *vring_new_virtqueue(unsigned int index,
-                                      unsigned int num,
-                                      unsigned int vring_align,
-                                      struct virtio_device *vdev,
-                                      bool weak_barriers,
-                                      void *pages,
-                                      bool (*notify)(struct virtqueue *),
-                                      void (*callback)(struct virtqueue *),
-                                      const char *name)
+struct virtqueue *__vring_new_virtqueue(unsigned int index,
+                                        struct vring vring,
+                                        struct virtio_device *vdev,
+                                        bool weak_barriers,
+                                        bool (*notify)(struct virtqueue *),
+                                        void (*callback)(struct virtqueue *),
+                                        const char *name)
 {
-        struct vring_virtqueue *vq;
         unsigned int i;
+        struct vring_virtqueue *vq;
 
-        /* We assume num is a power of 2. */
-        if (num & (num - 1)) {
-                dev_warn(&vdev->dev, "Bad virtqueue length %u\n", num);
-                return NULL;
-        }
-
-        vq = kmalloc(sizeof(*vq) + num * sizeof(struct vring_desc_state),
+        vq = kmalloc(sizeof(*vq) + vring.num * sizeof(struct vring_desc_state),
                      GFP_KERNEL);
         if (!vq)
                 return NULL;
 
-        vring_init(&vq->vring, num, pages, vring_align);
+        vq->vring = vring;
         vq->vq.callback = callback;
         vq->vq.vdev = vdev;
         vq->vq.name = name;
-        vq->vq.num_free = num;
+        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;
@@ -932,18 +932,145 @@ struct virtqueue *vring_new_virtqueue(unsigned int index,
 
         /* Put everything in free lists. */
         vq->free_head = 0;
-        for (i = 0; i < num-1; i++)
+        for (i = 0; i < vring.num-1; i++)
                 vq->vring.desc[i].next = cpu_to_virtio16(vdev, i + 1);
-        memset(vq->desc_state, 0, num * sizeof(struct vring_desc_state));
+        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 (*notify)(struct virtqueue *),
+        void (*callback)(struct virtqueue *),
+        const char *name)
+{
+        struct virtqueue *vq;
+        void *queue;
+        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,
+                                   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,
+                                      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,
+                                     notify, callback, name);
+}
 EXPORT_SYMBOL_GPL(vring_new_virtqueue);
 
-void vring_del_virtqueue(struct virtqueue *vq)
+void vring_del_virtqueue(struct virtqueue *_vq)
 {
-        list_del(&vq->list);
-        kfree(to_vvq(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);
 
@@ -1007,20 +1134,42 @@ void virtio_break_device(struct virtio_device *dev)
 }
 EXPORT_SYMBOL_GPL(virtio_break_device);
 
-void *virtqueue_get_avail(struct virtqueue *_vq)
+dma_addr_t virtqueue_get_desc_addr(struct virtqueue *_vq)
 {
         struct vring_virtqueue *vq = to_vvq(_vq);
 
-        return vq->vring.avail;
+        BUG_ON(!vq->we_own_ring);
+
+        return vq->queue_dma_addr;
 }
-EXPORT_SYMBOL_GPL(virtqueue_get_avail);
+EXPORT_SYMBOL_GPL(virtqueue_get_desc_addr);
 
-void *virtqueue_get_used(struct virtqueue *_vq)
+dma_addr_t virtqueue_get_avail_addr(struct virtqueue *_vq)
 {
         struct vring_virtqueue *vq = to_vvq(_vq);
 
-        return vq->vring.used;
+        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_used);
+EXPORT_SYMBOL_GPL(virtqueue_get_vring);
 
 MODULE_LICENSE("GPL");
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 8f4d4bfa6d46..d5eb5479a425 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -75,8 +75,27 @@ unsigned int virtqueue_get_vring_size(struct virtqueue *vq);
 
 bool virtqueue_is_broken(struct virtqueue *vq);
 
-void *virtqueue_get_avail(struct virtqueue *vq);
-void *virtqueue_get_used(struct virtqueue *vq);
+const struct vring *virtqueue_get_vring(struct virtqueue *vq);
+dma_addr_t virtqueue_get_desc_addr(struct virtqueue *vq);
+dma_addr_t virtqueue_get_avail_addr(struct virtqueue *vq);
+dma_addr_t virtqueue_get_used_addr(struct virtqueue *vq);
+
+/*
+ * Legacy accessors -- in almost all cases, these are the wrong functions
+ * to use.
+ */
+static inline void *virtqueue_get_desc(struct virtqueue *vq)
+{
+        return virtqueue_get_vring(vq)->desc;
+}
+static inline void *virtqueue_get_avail(struct virtqueue *vq)
+{
+        return virtqueue_get_vring(vq)->avail;
+}
+static inline void *virtqueue_get_used(struct virtqueue *vq)
+{
+        return virtqueue_get_vring(vq)->used;
+}
 
 /**
  * virtio_device - representation of a device using virtio
diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index a156e2b6ccfe..e8d36938f09a 100644
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h
@@ -59,6 +59,35 @@ static inline void virtio_store_mb(bool weak_barriers,
 struct virtio_device;
 struct virtqueue;
 
+/*
+ * Creates a virtqueue and allocates the descriptor ring.  If
+ * may_reduce_num is set, then this may allocate a smaller ring than
+ * expected.  The caller should query virtqueue_get_ring_size to learn
+ * the actual size of the ring.
+ */
+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 (*notify)(struct virtqueue *vq),
+                                         void (*callback)(struct virtqueue *vq),
+                                         const char *name);
+
+/* Creates a virtqueue with a custom layout. */
+struct virtqueue *__vring_new_virtqueue(unsigned int index,
+                                        struct vring vring,
+                                        struct virtio_device *vdev,
+                                        bool weak_barriers,
+                                        bool (*notify)(struct virtqueue *),
+                                        void (*callback)(struct virtqueue *),
+                                        const char *name);
+
+/*
+ * Creates a virtqueue with a standard layout but a caller-allocated
+ * ring.
+ */
 struct virtqueue *vring_new_virtqueue(unsigned int index,
                                       unsigned int num,
                                       unsigned int vring_align,
@@ -68,7 +97,13 @@ struct virtqueue *vring_new_virtqueue(unsigned int index,
                                       bool (*notify)(struct virtqueue *vq),
                                       void (*callback)(struct virtqueue *vq),
                                       const char *name);
+
+/*
+ * Destroys a virtqueue.  If created with vring_create_virtqueue, this
+ * also frees the ring.
+ */
 void vring_del_virtqueue(struct virtqueue *vq);
+
 /* Filter out transport-specific feature bits. */
 void vring_transport_features(struct virtio_device *vdev);