Subject: [PATCH RFC v8 02/11] vhost: use batched get_vq_desc version

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 11 Jun 2020 07:34:19 -0400

As testing shows no performance change, switch to that now.

Signed-off-by: Michael S. Tsirkin <[email-masked]>
Signed-off-by: Eugenio Pérez <[email-masked]>
Link: https://lore.kernel.org/r/[email-masked]
Signed-off-by: Michael S. Tsirkin <[email-masked]>
---
 drivers/vhost/test.c  |   2 +-
 drivers/vhost/vhost.c | 314 ++++++++----------------------------------
 drivers/vhost/vhost.h |   7 +-
 3 files changed, 61 insertions(+), 262 deletions(-)

diff --git a/drivers/vhost/test.c b/drivers/vhost/test.c
index 0466921f4772..7d69778aaa26 100644
--- a/drivers/vhost/test.c
+++ b/drivers/vhost/test.c
@@ -119,7 +119,7 @@ static int vhost_test_open(struct inode *inode, struct file *f)
 	dev = &n->dev;
 	vqs[VHOST_TEST_VQ] = &n->vqs[VHOST_TEST_VQ];
 	n->vqs[VHOST_TEST_VQ].handle_kick = handle_vq_kick;
-	vhost_dev_init(dev, vqs, VHOST_TEST_VQ_MAX, UIO_MAXIOV,
+	vhost_dev_init(dev, vqs, VHOST_TEST_VQ_MAX, UIO_MAXIOV + 64,
 		       VHOST_TEST_PKT_WEIGHT, VHOST_TEST_WEIGHT, true, NULL);
 
 	f->private_data = n;
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 11433d709651..dfcdb36d4227 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -304,6 +304,7 @@ static void vhost_vq_reset(struct vhost_dev *dev,
 {
 	vq->num = 1;
 	vq->ndescs = 0;
+	vq->first_desc = 0;
 	vq->desc = NULL;
 	vq->avail = NULL;
 	vq->used = NULL;
@@ -372,6 +373,11 @@ static int vhost_worker(void *data)
 	return 0;
 }
 
+static int vhost_vq_num_batch_descs(struct vhost_virtqueue *vq)
+{
+	return vq->max_descs - UIO_MAXIOV;
+}
+
 static void vhost_vq_free_iovecs(struct vhost_virtqueue *vq)
 {
 	kfree(vq->descs);
@@ -394,6 +400,9 @@ static long vhost_dev_alloc_iovecs(struct vhost_dev *dev)
 	for (i = 0; i < dev->nvqs; ++i) {
 		vq = dev->vqs[i];
 		vq->max_descs = dev->iov_limit;
+		if (vhost_vq_num_batch_descs(vq) < 0) {
+			return -EINVAL;
+		}
 		vq->descs = kmalloc_array(vq->max_descs,
 					  sizeof(*vq->descs),
 					  GFP_KERNEL);
@@ -1610,6 +1619,7 @@ long vhost_vring_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *arg
 		vq->last_avail_idx = s.num;
 		/* Forget the cached index value. */
 		vq->avail_idx = vq->last_avail_idx;
+		vq->ndescs = vq->first_desc = 0;
 		break;
 	case VHOST_GET_VRING_BASE:
 		s.index = idx;
@@ -2078,253 +2088,6 @@ static unsigned next_desc(struct vhost_virtqueue *vq, struct vring_desc *desc)
 	return next;
 }
 
-static int get_indirect(struct vhost_virtqueue *vq,
-			struct iovec iov[], unsigned int iov_size,
-			unsigned int *out_num, unsigned int *in_num,
-			struct vhost_log *log, unsigned int *log_num,
-			struct vring_desc *indirect)
-{
-	struct vring_desc desc;
-	unsigned int i = 0, count, found = 0;
-	u32 len = vhost32_to_cpu(vq, indirect->len);
-	struct iov_iter from;
-	int ret, access;
-
-	/* Sanity check */
-	if (unlikely(len % sizeof desc)) {
-		vq_err(vq, "Invalid length in indirect descriptor: "
-		       "len 0x%llx not multiple of 0x%zx\n",
-		       (unsigned long long)len,
-		       sizeof desc);
-		return -EINVAL;
-	}
-
-	ret = translate_desc(vq, vhost64_to_cpu(vq, indirect->addr), len, vq->indirect,
-			     UIO_MAXIOV, VHOST_ACCESS_RO);
-	if (unlikely(ret < 0)) {
-		if (ret != -EAGAIN)
-			vq_err(vq, "Translation failure %d in indirect.\n", ret);
-		return ret;
-	}
-	iov_iter_init(&from, READ, vq->indirect, ret, len);
-
-	/* We will use the result as an address to read from, so most
-	 * architectures only need a compiler barrier here. */
-	read_barrier_depends();
-
-	count = len / sizeof desc;
-	/* Buffers are chained via a 16 bit next field, so
-	 * we can have at most 2^16 of these. */
-	if (unlikely(count > USHRT_MAX + 1)) {
-		vq_err(vq, "Indirect buffer length too big: %d\n",
-		       indirect->len);
-		return -E2BIG;
-	}
-
-	do {
-		unsigned iov_count = *in_num + *out_num;
-		if (unlikely(++found > count)) {
-			vq_err(vq, "Loop detected: last one at %u "
-			       "indirect size %u\n",
-			       i, count);
-			return -EINVAL;
-		}
-		if (unlikely(!copy_from_iter_full(&desc, sizeof(desc), &from))) {
-			vq_err(vq, "Failed indirect descriptor: idx %d, %zx\n",
-			       i, (size_t)vhost64_to_cpu(vq, indirect->addr) + i * sizeof desc);
-			return -EINVAL;
-		}
-		if (unlikely(desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_INDIRECT))) {
-			vq_err(vq, "Nested indirect descriptor: idx %d, %zx\n",
-			       i, (size_t)vhost64_to_cpu(vq, indirect->addr) + i * sizeof desc);
-			return -EINVAL;
-		}
-
-		if (desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_WRITE))
-			access = VHOST_ACCESS_WO;
-		else
-			access = VHOST_ACCESS_RO;
-
-		ret = translate_desc(vq, vhost64_to_cpu(vq, desc.addr),
-				     vhost32_to_cpu(vq, desc.len), iov + iov_count,
-				     iov_size - iov_count, access);
-		if (unlikely(ret < 0)) {
-			if (ret != -EAGAIN)
-				vq_err(vq, "Translation failure %d indirect idx %d\n",
-					ret, i);
-			return ret;
-		}
-		/* If this is an input descriptor, increment that count. */
-		if (access == VHOST_ACCESS_WO) {
-			*in_num += ret;
-			if (unlikely(log && ret)) {
-				log[*log_num].addr = vhost64_to_cpu(vq, desc.addr);
-				log[*log_num].len = vhost32_to_cpu(vq, desc.len);
-				++*log_num;
-			}
-		} else {
-			/* If it's an output descriptor, they're all supposed
-			 * to come before any input descriptors. */
-			if (unlikely(*in_num)) {
-				vq_err(vq, "Indirect descriptor "
-				       "has out after in: idx %d\n", i);
-				return -EINVAL;
-			}
-			*out_num += ret;
-		}
-	} while ((i = next_desc(vq, &desc)) != -1);
-	return 0;
-}
-
-/* This looks in the virtqueue and for the first available buffer, and converts
- * it to an iovec for convenient access.  Since descriptors consist of some
- * number of output then some number of input descriptors, it's actually two
- * iovecs, but we pack them into one and note how many of each there were.
- *
- * This function returns the descriptor number found, or vq->num (which is
- * never a valid descriptor number) if none was found.  A negative code is
- * returned on error. */
-int vhost_get_vq_desc(struct vhost_virtqueue *vq,
-		      struct iovec iov[], unsigned int iov_size,
-		      unsigned int *out_num, unsigned int *in_num,
-		      struct vhost_log *log, unsigned int *log_num)
-{
-	struct vring_desc desc;
-	unsigned int i, head, found = 0;
-	u16 last_avail_idx;
-	__virtio16 avail_idx;
-	__virtio16 ring_head;
-	int ret, access;
-
-	/* Check it isn't doing very strange things with descriptor numbers. */
-	last_avail_idx = vq->last_avail_idx;
-
-	if (vq->avail_idx == vq->last_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;
-		}
-		vq->avail_idx = vhost16_to_cpu(vq, avail_idx);
-
-		if (unlikely((u16)(vq->avail_idx - last_avail_idx) > vq->num)) {
-			vq_err(vq, "Guest moved used index from %u to %u",
-				last_avail_idx, vq->avail_idx);
-			return -EFAULT;
-		}
-
-		/* If there's nothing new since last we looked, return
-		 * invalid.
-		 */
-		if (vq->avail_idx == last_avail_idx)
-			return vq->num;
-
-		/* Only get avail ring entries after they have been
-		 * exposed by guest.
-		 */
-		smp_rmb();
-	}
-
-	/* Grab the next descriptor number they're advertising, and increment
-	 * the index we've seen. */
-	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]);
-		return -EFAULT;
-	}
-
-	head = vhost16_to_cpu(vq, ring_head);
-
-	/* If their number is silly, that's an error. */
-	if (unlikely(head >= vq->num)) {
-		vq_err(vq, "Guest says index %u > %u is available",
-		       head, vq->num);
-		return -EINVAL;
-	}
-
-	/* When we start there are none of either input nor output. */
-	*out_num = *in_num = 0;
-	if (unlikely(log))
-		*log_num = 0;
-
-	i = head;
-	do {
-		unsigned iov_count = *in_num + *out_num;
-		if (unlikely(i >= vq->num)) {
-			vq_err(vq, "Desc index is %u > %u, head = %u",
-			       i, vq->num, head);
-			return -EINVAL;
-		}
-		if (unlikely(++found > vq->num)) {
-			vq_err(vq, "Loop detected: last one at %u "
-			       "vq size %u head %u\n",
-			       i, vq->num, head);
-			return -EINVAL;
-		}
-		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);
-			return -EFAULT;
-		}
-		if (desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_INDIRECT)) {
-			ret = get_indirect(vq, iov, iov_size,
-					   out_num, in_num,
-					   log, log_num, &desc);
-			if (unlikely(ret < 0)) {
-				if (ret != -EAGAIN)
-					vq_err(vq, "Failure detected "
-						"in indirect descriptor at idx %d\n", i);
-				return ret;
-			}
-			continue;
-		}
-
-		if (desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_WRITE))
-			access = VHOST_ACCESS_WO;
-		else
-			access = VHOST_ACCESS_RO;
-		ret = translate_desc(vq, vhost64_to_cpu(vq, desc.addr),
-				     vhost32_to_cpu(vq, desc.len), iov + iov_count,
-				     iov_size - iov_count, access);
-		if (unlikely(ret < 0)) {
-			if (ret != -EAGAIN)
-				vq_err(vq, "Translation failure %d descriptor idx %d\n",
-					ret, i);
-			return ret;
-		}
-		if (access == VHOST_ACCESS_WO) {
-			/* If this is an input descriptor,
-			 * increment that count. */
-			*in_num += ret;
-			if (unlikely(log && ret)) {
-				log[*log_num].addr = vhost64_to_cpu(vq, desc.addr);
-				log[*log_num].len = vhost32_to_cpu(vq, desc.len);
-				++*log_num;
-			}
-		} else {
-			/* If it's an output descriptor, they're all supposed
-			 * to come before any input descriptors. */
-			if (unlikely(*in_num)) {
-				vq_err(vq, "Descriptor has out after in: "
-				       "idx %d\n", i);
-				return -EINVAL;
-			}
-			*out_num += ret;
-		}
-	} while ((i = next_desc(vq, &desc)) != -1);
-
-	/* On success, increment avail index. */
-	vq->last_avail_idx++;
-
-	/* Assume notifications from guest are disabled at this point,
-	 * if they aren't we would need to update avail_event index. */
-	BUG_ON(!(vq->used_flags & VRING_USED_F_NO_NOTIFY));
-	return head;
-}
-EXPORT_SYMBOL_GPL(vhost_get_vq_desc);
-
 static struct vhost_desc *peek_split_desc(struct vhost_virtqueue *vq)
 {
 	BUG_ON(!vq->ndescs);
@@ -2428,7 +2191,7 @@ static int fetch_indirect_descs(struct vhost_virtqueue *vq,
 
 /* This function returns a value > 0 if a descriptor was found, or 0 if none were found.
  * A negative code is returned on error. */
-static int fetch_descs(struct vhost_virtqueue *vq)
+static int fetch_buf(struct vhost_virtqueue *vq)
 {
 	unsigned int i, head, found = 0;
 	struct vhost_desc *last;
@@ -2441,7 +2204,7 @@ static int fetch_descs(struct vhost_virtqueue *vq)
 	/* Check it isn't doing very strange things with descriptor numbers. */
 	last_avail_idx = vq->last_avail_idx;
 
-	if (vq->avail_idx == vq->last_avail_idx) {
+	if (unlikely(vq->avail_idx == vq->last_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);
@@ -2532,6 +2295,41 @@ static int fetch_descs(struct vhost_virtqueue *vq)
 	return 1;
 }
 
+/* This function returns a value > 0 if a descriptor was found, or 0 if none were found.
+ * A negative code is returned on error. */
+static int fetch_descs(struct vhost_virtqueue *vq)
+{
+	int ret;
+
+	if (unlikely(vq->first_desc >= vq->ndescs)) {
+		vq->first_desc = 0;
+		vq->ndescs = 0;
+	}
+
+	if (vq->ndescs)
+		return 1;
+
+	for (ret = 1;
+	     ret > 0 && vq->ndescs <= vhost_vq_num_batch_descs(vq);
+	     ret = fetch_buf(vq))
+		;
+
+	/* On success we expect some descs */
+	BUG_ON(ret > 0 && !vq->ndescs);
+	return ret;
+}
+
+/* Reverse the effects of fetch_descs */
+static void unfetch_descs(struct vhost_virtqueue *vq)
+{
+	int i;
+
+	for (i = vq->first_desc; i < vq->ndescs; ++i)
+		if (!(vq->descs[i].flags & VRING_DESC_F_NEXT))
+			vq->last_avail_idx -= 1;
+	vq->ndescs = 0;
+}
+
 /* This looks in the virtqueue and for the first available buffer, and converts
  * it to an iovec for convenient access.  Since descriptors consist of some
  * number of output then some number of input descriptors, it's actually two
@@ -2540,7 +2338,7 @@ static int fetch_descs(struct vhost_virtqueue *vq)
  * This function returns the descriptor number found, or vq->num (which is
  * never a valid descriptor number) if none was found.  A negative code is
  * returned on error. */
-int vhost_get_vq_desc_batch(struct vhost_virtqueue *vq,
+int vhost_get_vq_desc(struct vhost_virtqueue *vq,
 		      struct iovec iov[], unsigned int iov_size,
 		      unsigned int *out_num, unsigned int *in_num,
 		      struct vhost_log *log, unsigned int *log_num)
@@ -2549,7 +2347,7 @@ int vhost_get_vq_desc_batch(struct vhost_virtqueue *vq,
 	int i;
 
 	if (ret <= 0)
-		goto err_fetch;
+		goto err;
 
 	/* Now convert to IOV */
 	/* When we start there are none of either input nor output. */
@@ -2557,7 +2355,7 @@ int vhost_get_vq_desc_batch(struct vhost_virtqueue *vq,
 	if (unlikely(log))
 		*log_num = 0;
 
-	for (i = 0; i < vq->ndescs; ++i) {
+	for (i = vq->first_desc; i < vq->ndescs; ++i) {
 		unsigned iov_count = *in_num + *out_num;
 		struct vhost_desc *desc = &vq->descs[i];
 		int access;
@@ -2603,24 +2401,26 @@ int vhost_get_vq_desc_batch(struct vhost_virtqueue *vq,
 		}
 
 		ret = desc->id;
+
+		if (!(desc->flags & VRING_DESC_F_NEXT))
+			break;
 	}
 
-	vq->ndescs = 0;
+	vq->first_desc = i + 1;
 
 	return ret;
 
 err:
-	vhost_discard_vq_desc(vq, 1);
-err_fetch:
-	vq->ndescs = 0;
+	unfetch_descs(vq);
 
 	return ret ? ret : vq->num;
 }
-EXPORT_SYMBOL_GPL(vhost_get_vq_desc_batch);
+EXPORT_SYMBOL_GPL(vhost_get_vq_desc);
 
 /* Reverse the effect of vhost_get_vq_desc. Useful for error handling. */
 void vhost_discard_vq_desc(struct vhost_virtqueue *vq, int n)
 {
+	unfetch_descs(vq);
 	vq->last_avail_idx -= n;
 }
 EXPORT_SYMBOL_GPL(vhost_discard_vq_desc);
diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
index 87089d51490d..fed36af5c444 100644
--- a/drivers/vhost/vhost.h
+++ b/drivers/vhost/vhost.h
@@ -81,6 +81,7 @@ struct vhost_virtqueue {
 
 	struct vhost_desc *descs;
 	int ndescs;
+	int first_desc;
 	int max_descs;
 
 	struct file *kick;
@@ -189,10 +190,6 @@ long vhost_vring_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *arg
 bool vhost_vq_access_ok(struct vhost_virtqueue *vq);
 bool vhost_log_access_ok(struct vhost_dev *);
 
-int vhost_get_vq_desc_batch(struct vhost_virtqueue *,
-		      struct iovec iov[], unsigned int iov_count,
-		      unsigned int *out_num, unsigned int *in_num,
-		      struct vhost_log *log, unsigned int *log_num);
 int vhost_get_vq_desc(struct vhost_virtqueue *,
 		      struct iovec iov[], unsigned int iov_count,
 		      unsigned int *out_num, unsigned int *in_num,
@@ -261,6 +258,8 @@ static inline void vhost_vq_set_backend(struct vhost_virtqueue *vq,
 					void *private_data)
 {
 	vq->private_data = private_data;
+	vq->ndescs = 0;
+	vq->first_desc = 0;
 }
 
 /**
-- 
MST