Re: [RFC PATCH V2 2/5] vhost: fine grain userspace memory accessors

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On 2019/3/6 下午6:45, Christophe de Dinechin wrote:

On 6 Mar 2019, at 08:18, Jason Wang <jasowang@xxxxxxxxxx> wrote:

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@xxxxxxxxxx>
---
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 400aa78..29709e7 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -869,6 +869,34 @@ 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; \
@@ -907,6 +935,43 @@ 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)
@@ -1840,8 +1905,7 @@ 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. */
@@ -1858,8 +1922,7 @@ 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;
@@ -1895,7 +1958,7 @@ 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);
 From the error case, it looks like you are not entirely encapsulating
knowledge of what the accessor uses, i.e. it’s not:

		vq_err(vq, "Can't access used idx at %p\n",
		       &last_user_idx);

Maybe move error message within accessor?


Good catch. Will fix but I still prefer to keep the place of vq_err(). Moving error message (if needed) could be done in the future.

Thanks



@@ -2094,7 +2157,7 @@ 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;
Same here.

@@ -2121,8 +2184,7 @@ 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]);
@@ -2157,8 +2219,7 @@ 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);
@@ -2251,7 +2312,7 @@ 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;
	}
@@ -2293,8 +2354,7 @@ 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;
	}
@@ -2327,7 +2387,7 @@ 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;
		}
@@ -2341,7 +2401,7 @@ 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;
	}
@@ -2386,7 +2446,7 @@ 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);
@@ -2422,7 +2482,7 @@ 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);
--
1.8.3.1




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