[RFC PATCH 3/4] vhost: byteswap virtqueue attributes

Cédric Le Goater
2014-10-29T08:38:44Z

The virtqueue structure shares a few attributes with the guest OS
which need to be byteswapped when the endian order of the host is
different.

This patch uses the vq->byteswap attribute to decide whether to
byteswap or not data being accessed in the guest memory.

Signed-off-by: Cédric Le Goater <clg@fr.ibm.com>
---
drivers/vhost/vhost.c | 52 +++++++++++++++++++++++++++++++++++++------------
1 file changed, 40 insertions(+), 12 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index afcb3368370c..9a538f4d2ff1 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1097,7 +1097,7 @@ static void vring_desc_swap(struct vring_desc *desc)
static int vhost_update_used_flags(struct vhost_virtqueue *vq)
{
void __user *used;
- if (__put_user(vq->used_flags, &vq->used->flags) < 0)
+ if (__vq_put_user(vq, vq->used_flags, &vq->used->flags) < 0)
return -EFAULT;
if (unlikely(vq->log_used)) {
/* Make sure the flag is seen before log. */
@@ -1115,7 +1115,7 @@ static int vhost_update_used_flags(struct vhost_virtqueue *vq)

static int vhost_update_avail_event(struct vhost_virtqueue *vq, u16 avail_event)
{
- if (__put_user(vq->avail_idx, vhost_avail_event(vq)))
+ if (__vq_put_user(vq, vq->avail_idx, vhost_avail_event(vq)))
return -EFAULT;
if (unlikely(vq->log_used)) {
void __user *used;
@@ -1142,7 +1142,7 @@ int vhost_init_used(struct vhost_virtqueue *vq)
if (r)
return r;
vq->signalled_used_valid = false;
- return get_user(vq->last_used_idx, &vq->used->idx);
+ return vq_get_user(vq, vq->last_used_idx, &vq->used->idx);
}
EXPORT_SYMBOL_GPL(vhost_init_used);

@@ -1254,6 +1254,10 @@ static int get_indirect(struct vhost_virtqueue *vq,
i, (size_t)indirect->addr + i * sizeof desc);
return -EINVAL;
}
+
+ if (vq->byteswap)
+ vring_desc_swap(&desc);
+
if (unlikely(desc.flags & VRING_DESC_F_INDIRECT)) {
vq_err(vq, "Nested indirect descriptor: idx %d, %zx\n",
i, (size_t)indirect->addr + i * sizeof desc);
@@ -1309,7 +1313,7 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,

/* Check it isn't doing very strange things with descriptor numbers. */
last_avail_idx = vq->last_avail_idx;
- if (unlikely(__get_user(vq->avail_idx, &vq->avail->idx))) {
+ if (unlikely(__vq_get_user(vq, vq->avail_idx, &vq->avail->idx))) {
vq_err(vq, "Failed to access avail idx at %p\n",
&vq->avail->idx);
return -EFAULT;
@@ -1330,7 +1334,7 @@ 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(__get_user(head,
+ if (unlikely(__vq_get_user(vq, head,
&vq->avail->ring[last_avail_idx % vq->num]))) {
vq_err(vq, "Failed to read head: idx %d address %p\n",
last_avail_idx,
@@ -1370,6 +1374,10 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
i, vq->desc + i);
return -EFAULT;
}
+
+ if (vq->byteswap)
+ vring_desc_swap(&desc);
+
if (desc.flags & VRING_DESC_F_INDIRECT) {
ret = get_indirect(vq, iov, iov_size,
out_num, in_num,
@@ -1437,6 +1445,26 @@ int vhost_add_used(struct vhost_virtqueue *vq, unsigned int head, int len)
}
EXPORT_SYMBOL_GPL(vhost_add_used);

+static int __copyhead_to_user(struct vhost_virtqueue *vq,
+ struct vring_used_elem *heads,
+ struct vring_used_elem __user *used,
+ unsigned count)
+{
+ int i;
+
+ for (i = 0; i < count; i++) {
+ if (__vq_put_user(vq, heads[i].id, &used[i].id)) {
+ vq_err(vq, "Failed to write used id");
+ return -EFAULT;
+ }
+ if (__vq_put_user(vq, heads[i].len, &used[i].len)) {
+ vq_err(vq, "Failed to write used len");
+ return -EFAULT;
+ }
+ }
+ return 0;
+}
+
static int __vhost_add_used_n(struct vhost_virtqueue *vq,
struct vring_used_elem *heads,
unsigned count)
@@ -1448,15 +1476,15 @@ static int __vhost_add_used_n(struct vhost_virtqueue *vq,
start = vq->last_used_idx % vq->num;
used = vq->used->ring + start;
if (count == 1) {
- if (__put_user(heads[0].id, &used->id)) {
+ if (__vq_put_user(vq, heads[0].id, &used->id)) {
vq_err(vq, "Failed to write used id");
return -EFAULT;
}
- if (__put_user(heads[0].len, &used->len)) {
+ if (__vq_put_user(vq, heads[0].len, &used->len)) {
vq_err(vq, "Failed to write used len");
return -EFAULT;
}
- } else if (__copy_to_user(used, heads, count * sizeof *used)) {
+ } else if (__copyhead_to_user(vq, heads, used, count)) {
vq_err(vq, "Failed to write used");
return -EFAULT;
}
@@ -1500,7 +1528,7 @@ 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 (put_user(vq->last_used_idx, &vq->used->idx)) {
+ if (vq_put_user(vq, vq->last_used_idx, &vq->used->idx)) {
vq_err(vq, "Failed to increment used idx");
return -EFAULT;
}
@@ -1531,7 +1559,7 @@ static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)

if (!vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX)) {
__u16 flags;
- if (__get_user(flags, &vq->avail->flags)) {
+ if (__vq_get_user(vq, flags, &vq->avail->flags)) {
vq_err(vq, "Failed to get flags");
return true;
}
@@ -1545,7 +1573,7 @@ static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
if (unlikely(!v))
return true;

- if (get_user(event, vhost_used_event(vq))) {
+ if (vq_get_user(vq, event, vhost_used_event(vq))) {
vq_err(vq, "Failed to get used event idx");
return true;
}
@@ -1608,7 +1636,7 @@ 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 = __get_user(avail_idx, &vq->avail->idx);
+ r = __vq_get_user(vq, avail_idx, &vq->avail->idx);
if (r) {
vq_err(vq, "Failed to check avail idx at %p: %d\n",
&vq->avail->idx, r);
--
1.7.10.4