vhost: fine grain userspace memory accessors [Linux 5.3]

This Linux kernel change "vhost: fine grain userspace memory accessors" is included in the Linux 5.3 release. This change is authored by Jason Wang <jasowang [at] redhat.com> on Fri May 24 04:12:14 2019 -0400. The commit for this change in Linux stable tree is 7b5d753 (patch).

vhost: fine grain userspace memory accessors

This is used to hide the metadata address from virtqueue helpers. This
will allow to implement a vmap based fast accessing to metadata.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

There are 94 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/vhost/vhost.c | 94 +++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 77 insertions(+), 17 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 3fb5801..b89faed 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -887,6 +887,34 @@ static inline void __user *__vhost_get_user(struct vhost_virtqueue *vq,
    ret; \
 })

+static inline int vhost_put_avail_event(struct vhost_virtqueue *vq)
+{
+   return vhost_put_user(vq, cpu_to_vhost16(vq, vq->avail_idx),
+                 vhost_avail_event(vq));
+}
+
+static inline int vhost_put_used(struct vhost_virtqueue *vq,
+                struct vring_used_elem *head, int idx,
+                int count)
+{
+   return vhost_copy_to_user(vq, vq->used->ring + idx, head,
+                 count * sizeof(*head));
+}
+
+static inline int vhost_put_used_flags(struct vhost_virtqueue *vq)
+
+{
+   return vhost_put_user(vq, cpu_to_vhost16(vq, vq->used_flags),
+                 &vq->used->flags);
+}
+
+static inline int vhost_put_used_idx(struct vhost_virtqueue *vq)
+
+{
+   return vhost_put_user(vq, cpu_to_vhost16(vq, vq->last_used_idx),
+                 &vq->used->idx);
+}
+
 #define vhost_get_user(vq, x, ptr, type)       \
 ({ \
    int ret; \
@@ -925,6 +953,43 @@ static void vhost_dev_unlock_vqs(struct vhost_dev *d)
        mutex_unlock(&d->vqs[i]->mutex);
 }

+static inline int vhost_get_avail_idx(struct vhost_virtqueue *vq,
+                     __virtio16 *idx)
+{
+   return vhost_get_avail(vq, *idx, &vq->avail->idx);
+}
+
+static inline int vhost_get_avail_head(struct vhost_virtqueue *vq,
+                      __virtio16 *head, int idx)
+{
+   return vhost_get_avail(vq, *head,
+                  &vq->avail->ring[idx & (vq->num - 1)]);
+}
+
+static inline int vhost_get_avail_flags(struct vhost_virtqueue *vq,
+                   __virtio16 *flags)
+{
+   return vhost_get_avail(vq, *flags, &vq->avail->flags);
+}
+
+static inline int vhost_get_used_event(struct vhost_virtqueue *vq,
+                      __virtio16 *event)
+{
+   return vhost_get_avail(vq, *event, vhost_used_event(vq));
+}
+
+static inline int vhost_get_used_idx(struct vhost_virtqueue *vq,
+                    __virtio16 *idx)
+{
+   return vhost_get_used(vq, *idx, &vq->used->idx);
+}
+
+static inline int vhost_get_desc(struct vhost_virtqueue *vq,
+                struct vring_desc *desc, int idx)
+{
+   return vhost_copy_from_user(vq, desc, vq->desc + idx, sizeof(*desc));
+}
+
 static int vhost_new_umem_range(struct vhost_umem *umem,
                u64 start, u64 size, u64 end,
                u64 userspace_addr, int perm)
@@ -1862,8 +1927,7 @@ int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
 static int vhost_update_used_flags(struct vhost_virtqueue *vq)
 {
    void __user *used;
-   if (vhost_put_user(vq, cpu_to_vhost16(vq, vq->used_flags),
-              &vq->used->flags) < 0)
+   if (vhost_put_used_flags(vq))
        return -EFAULT;
    if (unlikely(vq->log_used)) {
        /* Make sure the flag is seen before log. */
@@ -1880,8 +1944,7 @@ static int vhost_update_used_flags(struct vhost_virtqueue *vq)

 static int vhost_update_avail_event(struct vhost_virtqueue *vq, u16 avail_event)
 {
-   if (vhost_put_user(vq, cpu_to_vhost16(vq, vq->avail_idx),
-              vhost_avail_event(vq)))
+   if (vhost_put_avail_event(vq))
        return -EFAULT;
    if (unlikely(vq->log_used)) {
        void __user *used;
@@ -1917,7 +1980,7 @@ int vhost_vq_init_access(struct vhost_virtqueue *vq)
        r = -EFAULT;
        goto err;
    }
-   r = vhost_get_used(vq, last_used_idx, &vq->used->idx);
+   r = vhost_get_used_idx(vq, &last_used_idx);
    if (r) {
        vq_err(vq, "Can't access used idx at %p\n",
               &vq->used->idx);
@@ -2116,7 +2179,7 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
    last_avail_idx = vq->last_avail_idx;

    if (vq->avail_idx == vq->last_avail_idx) {
-       if (unlikely(vhost_get_avail(vq, avail_idx, &vq->avail->idx))) {
+       if (unlikely(vhost_get_avail_idx(vq, &avail_idx))) {
            vq_err(vq, "Failed to access avail idx at %p\n",
                &vq->avail->idx);
            return -EFAULT;
@@ -2143,8 +2206,7 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,

    /* Grab the next descriptor number they're advertising, and increment
     * the index we've seen. */
-   if (unlikely(vhost_get_avail(vq, ring_head,
-            &vq->avail->ring[last_avail_idx & (vq->num - 1)]))) {
+   if (unlikely(vhost_get_avail_head(vq, &ring_head, last_avail_idx))) {
        vq_err(vq, "Failed to read head: idx %d address %p\n",
               last_avail_idx,
               &vq->avail->ring[last_avail_idx % vq->num]);
@@ -2179,8 +2241,7 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
                   i, vq->num, head);
            return -EINVAL;
        }
-       ret = vhost_copy_from_user(vq, &desc, vq->desc + i,
-                      sizeof desc);
+       ret = vhost_get_desc(vq, &desc, i);
        if (unlikely(ret)) {
            vq_err(vq, "Failed to get descriptor: idx %d addr %p\n",
                   i, vq->desc + i);
@@ -2273,7 +2334,7 @@ static int __vhost_add_used_n(struct vhost_virtqueue *vq,

    start = vq->last_used_idx & (vq->num - 1);
    used = vq->used->ring + start;
-   if (vhost_copy_to_user(vq, used, heads, count * sizeof *used)) {
+   if (vhost_put_used(vq, heads, start, count)) {
        vq_err(vq, "Failed to write used");
        return -EFAULT;
    }
@@ -2315,8 +2376,7 @@ int vhost_add_used_n(struct vhost_virtqueue *vq, struct vring_used_elem *heads,

    /* Make sure buffer is written before we update index. */
    smp_wmb();
-   if (vhost_put_user(vq, cpu_to_vhost16(vq, vq->last_used_idx),
-              &vq->used->idx)) {
+   if (vhost_put_used_idx(vq)) {
        vq_err(vq, "Failed to increment used idx");
        return -EFAULT;
    }
@@ -2349,7 +2409,7 @@ static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)

    if (!vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX)) {
        __virtio16 flags;
-       if (vhost_get_avail(vq, flags, &vq->avail->flags)) {
+       if (vhost_get_avail_flags(vq, &flags)) {
            vq_err(vq, "Failed to get flags");
            return true;
        }
@@ -2363,7 +2423,7 @@ static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
    if (unlikely(!v))
        return true;

-   if (vhost_get_avail(vq, event, vhost_used_event(vq))) {
+   if (vhost_get_used_event(vq, &event)) {
        vq_err(vq, "Failed to get used event idx");
        return true;
    }
@@ -2408,7 +2468,7 @@ bool vhost_vq_avail_empty(struct vhost_dev *dev, struct vhost_virtqueue *vq)
    if (vq->avail_idx != vq->last_avail_idx)
        return false;

-   r = vhost_get_avail(vq, avail_idx, &vq->avail->idx);
+   r = vhost_get_avail_idx(vq, &avail_idx);
    if (unlikely(r))
        return false;
    vq->avail_idx = vhost16_to_cpu(vq, avail_idx);
@@ -2444,7 +2504,7 @@ bool vhost_enable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
    /* They could have slipped one in as we were doing that: make
     * sure it's written, then check again. */
    smp_mb();
-   r = vhost_get_avail(vq, avail_idx, &vq->avail->idx);
+   r = vhost_get_avail_idx(vq, &avail_idx);
    if (r) {
        vq_err(vq, "Failed to check avail idx at %p: %d\n",
               &vq->avail->idx, r);

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