[PATCH 0/4] vhost: Cleanup

[PATCH 0/4] vhost: Cleanup

[Gavin Shan]

This is suggested by Michael S. Tsirkin according to [1] and the goal
is to apply smp_rmb() inside vhost_get_avail_idx() if needed. With it,
the caller of the function needn't to worry about memory barriers. Since
we're here, other cleanups are also applied.

[1] https://lore.kernel.org/virtualization/20240327075940-mutt-send-email-mst@kernel.org/

PATCH[1] drops the local variable @last_avail_idx since it's equivalent
         to vq->last_avail_idx
PATCH[2] improves vhost_get_avail_idx() so that smp_rmb() is applied if
         needed. Besides, the sanity checks on the retrieved available
         queue index are also squeezed to vhost_get_avail_idx()
PATCH[3] improves vhost_get_avail_head(), similar to what we're doing
         for vhost_get_avail_idx(), so that the relevant sanity checks
         on the head are squeezed to vhost_get_avail_head()
PATCH[4] Reformat vhost_{get, put}_user() by using tab instead of space
         as the terminator for each line

Gavin Shan (4):
  vhost: Drop variable last_avail_idx in vhost_get_vq_desc()
  vhost: Improve vhost_get_avail_idx() with smp_rmb()
  vhost: Improve vhost_get_avail_head()
  vhost: Reformat vhost_{get, put}_user()

 drivers/vhost/vhost.c | 199 +++++++++++++++++++-----------------------
 1 file changed, 88 insertions(+), 111 deletions(-)

-- 
2.44.0

[PATCH 1/4] vhost: Drop variable last_avail_idx in vhost_get_vq_desc()

[Gavin Shan]

The local variable @last_avail_idx is equivalent to vq->last_avail_idx.
So the code can be simplified a bit by dropping the local variable
@last_avail_idx.

No functional change intended.

Signed-off-by: Gavin Shan <gshan@redhat.com>
---
 drivers/vhost/vhost.c | 15 ++++++---------
 1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 8995730ce0bf..ef7942103232 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2498,14 +2498,11 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
 {
 	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",
@@ -2514,16 +2511,16 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
 		}
 		vq->avail_idx = vhost16_to_cpu(vq, avail_idx);
 
-		if (unlikely((u16)(vq->avail_idx - last_avail_idx) > vq->num)) {
+		if (unlikely((u16)(vq->avail_idx - vq->last_avail_idx) > vq->num)) {
 			vq_err(vq, "Guest moved avail index from %u to %u",
-				last_avail_idx, vq->avail_idx);
+				vq->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)
+		if (vq->avail_idx == vq->last_avail_idx)
 			return vq->num;
 
 		/* Only get avail ring entries after they have been
@@ -2534,10 +2531,10 @@ 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_head(vq, &ring_head, last_avail_idx))) {
+	if (unlikely(vhost_get_avail_head(vq, &ring_head, vq->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]);
+		       vq->last_avail_idx,
+		       &vq->avail->ring[vq->last_avail_idx % vq->num]);
 		return -EFAULT;
 	}
 
-- 
2.44.0

[PATCH 2/4] vhost: Improve vhost_get_avail_idx() with smp_rmb()

[Gavin Shan]

All the callers of vhost_get_avail_idx() are concerned to the memory
barrier, imposed by smp_rmb() to ensure the order of the available
ring entry read and avail_idx read.

Improve vhost_get_avail_idx() so that smp_rmb() is executed when
the avail_idx is advanced. With it, the callers needn't to worry
about the memory barrier.

No functional change intended.

Suggested-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Gavin Shan <gshan@redhat.com>
---
 drivers/vhost/vhost.c | 91 ++++++++++++++++---------------------------
 1 file changed, 34 insertions(+), 57 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index ef7942103232..b3adc0bc9e72 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1290,10 +1290,34 @@ 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)
+static inline int vhost_get_avail_idx(struct vhost_virtqueue *vq)
 {
-	return vhost_get_avail(vq, *idx, &vq->avail->idx);
+	__virtio16 avail_idx;
+	int r;
+
+	r = vhost_get_avail(vq, avail_idx, &vq->avail->idx);
+	if (unlikely(r)) {
+		vq_err(vq, "Failed to access avail idx at %p\n",
+		       &vq->avail->idx);
+		return r;
+	}
+
+	vq->avail_idx = vhost16_to_cpu(vq, avail_idx);
+	if (vq->avail_idx != vq->last_avail_idx) {
+		/* Ensure the available ring entry read happens
+		 * before the avail_idx read when the avail_idx
+		 * is advanced.
+		 */
+		smp_rmb();
+	}
+
+	if (unlikely((u16)(vq->avail_idx - vq->last_avail_idx) > vq->num)) {
+		vq_err(vq, "Invalid avail index change from %u to %u",
+		       vq->last_avail_idx, vq->avail_idx);
+		return -EINVAL;
+	}
+
+	return 0;
 }
 
 static inline int vhost_get_avail_head(struct vhost_virtqueue *vq,
@@ -2498,35 +2522,19 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
 {
 	struct vring_desc desc;
 	unsigned int i, head, found = 0;
-	__virtio16 avail_idx;
 	__virtio16 ring_head;
 	int ret, access;
 
-	/* Check it isn't doing very strange things with descriptor numbers. */
 	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 - vq->last_avail_idx) > vq->num)) {
-			vq_err(vq, "Guest moved avail index from %u to %u",
-				vq->last_avail_idx, vq->avail_idx);
-			return -EFAULT;
-		}
+		ret = vhost_get_avail_idx(vq);
+		if (unlikely(ret))
+			return ret;
 
 		/* If there's nothing new since last we looked, return
 		 * invalid.
 		 */
 		if (vq->avail_idx == vq->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
@@ -2787,35 +2795,19 @@ EXPORT_SYMBOL_GPL(vhost_add_used_and_signal_n);
 /* return true if we're sure that avaiable ring is empty */
 bool vhost_vq_avail_empty(struct vhost_dev *dev, struct vhost_virtqueue *vq)
 {
-	__virtio16 avail_idx;
-	int r;
-
 	if (vq->avail_idx != vq->last_avail_idx)
 		return false;
 
-	r = vhost_get_avail_idx(vq, &avail_idx);
-	if (unlikely(r))
-		return false;
-
-	vq->avail_idx = vhost16_to_cpu(vq, avail_idx);
-	if (vq->avail_idx != vq->last_avail_idx) {
-		/* Since we have updated avail_idx, the following
-		 * call to vhost_get_vq_desc() will read available
-		 * ring entries. Make sure that read happens after
-		 * the avail_idx read.
-		 */
-		smp_rmb();
+	if (unlikely(vhost_get_avail_idx(vq)))
 		return false;
-	}
 
-	return true;
+	return vq->avail_idx == vq->last_avail_idx;
 }
 EXPORT_SYMBOL_GPL(vhost_vq_avail_empty);
 
 /* OK, now we need to know about added descriptors. */
 bool vhost_enable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
 {
-	__virtio16 avail_idx;
 	int r;
 
 	if (!(vq->used_flags & VRING_USED_F_NO_NOTIFY))
@@ -2839,25 +2831,10 @@ 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_idx(vq, &avail_idx);
-	if (r) {
-		vq_err(vq, "Failed to check avail idx at %p: %d\n",
-		       &vq->avail->idx, r);
+	if (unlikely(vhost_get_avail_idx(vq)))
 		return false;
-	}
-
-	vq->avail_idx = vhost16_to_cpu(vq, avail_idx);
-	if (vq->avail_idx != vq->last_avail_idx) {
-		/* Since we have updated avail_idx, the following
-		 * call to vhost_get_vq_desc() will read available
-		 * ring entries. Make sure that read happens after
-		 * the avail_idx read.
-		 */
-		smp_rmb();
-		return true;
-	}
 
-	return false;
+	return vq->avail_idx != vq->last_avail_idx;
 }
 EXPORT_SYMBOL_GPL(vhost_enable_notify);
 
-- 
2.44.0

[PATCH 3/4] vhost: Improve vhost_get_avail_head()

[Gavin Shan]

Improve vhost_get_avail_head() so that the head or errno is returned.
With it, the relevant sanity checks are squeezed to vhost_get_avail_head()
and vhost_get_vq_desc() is further simplified.

No functional change intended.

Signed-off-by: Gavin Shan <gshan@redhat.com>
---
 drivers/vhost/vhost.c | 43 +++++++++++++++++++++++--------------------
 1 file changed, 23 insertions(+), 20 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index b3adc0bc9e72..a3de9325175f 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1320,11 +1320,27 @@ static inline int vhost_get_avail_idx(struct vhost_virtqueue *vq)
 	return 0;
 }
 
-static inline int vhost_get_avail_head(struct vhost_virtqueue *vq,
-				       __virtio16 *head, int idx)
+static inline int vhost_get_avail_head(struct vhost_virtqueue *vq)
 {
-	return vhost_get_avail(vq, *head,
-			       &vq->avail->ring[idx & (vq->num - 1)]);
+	__virtio16 head;
+	int r;
+
+	r = vhost_get_avail(vq, head,
+			    &vq->avail->ring[vq->last_avail_idx & (vq->num - 1)]);
+	if (unlikely(r)) {
+		vq_err(vq, "Failed to read head: idx %u address %p\n",
+		       vq->last_avail_idx,
+		       &vq->avail->ring[vq->last_avail_idx % vq->num]);
+		return r;
+	}
+
+	r = vhost16_to_cpu(vq, head);
+	if (unlikely(r >= vq->num)) {
+		vq_err(vq, "Invalid head %d (%u)\n", r, vq->num);
+		return -EINVAL;
+	}
+
+	return r;
 }
 
 static inline int vhost_get_avail_flags(struct vhost_virtqueue *vq,
@@ -2522,7 +2538,6 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
 {
 	struct vring_desc desc;
 	unsigned int i, head, found = 0;
-	__virtio16 ring_head;
 	int ret, access;
 
 	if (vq->avail_idx == vq->last_avail_idx) {
@@ -2539,21 +2554,9 @@ 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_head(vq, &ring_head, vq->last_avail_idx))) {
-		vq_err(vq, "Failed to read head: idx %d address %p\n",
-		       vq->last_avail_idx,
-		       &vq->avail->ring[vq->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;
-	}
+	head = vhost_get_avail_head(vq);
+	if (unlikely(head < 0))
+		return head;
 
 	/* When we start there are none of either input nor output. */
 	*out_num = *in_num = 0;
-- 
2.44.0

[PATCH 4/4] vhost: Reformat vhost_{get, put}_user()

[Gavin Shan]

Reformat the macros to use tab as the terminator for each line so
that it looks clean.

No functional change intended.

Signed-off-by: Gavin Shan <gshan@redhat.com>
---
 drivers/vhost/vhost.c | 60 +++++++++++++++++++++----------------------
 1 file changed, 30 insertions(+), 30 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index a3de9325175f..3be19877f9df 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1207,21 +1207,22 @@ static inline void __user *__vhost_get_user(struct vhost_virtqueue *vq,
 	return __vhost_get_user_slow(vq, addr, size, type);
 }
 
-#define vhost_put_user(vq, x, ptr)		\
-({ \
-	int ret; \
-	if (!vq->iotlb) { \
-		ret = __put_user(x, ptr); \
-	} else { \
-		__typeof__(ptr) to = \
+#define vhost_put_user(vq, x, ptr)					\
+({									\
+	int ret;							\
+	if (!vq->iotlb) {						\
+		ret = __put_user(x, ptr);				\
+	} else {							\
+		__typeof__(ptr) to =					\
 			(__typeof__(ptr)) __vhost_get_user(vq, ptr,	\
-					  sizeof(*ptr), VHOST_ADDR_USED); \
-		if (to != NULL) \
-			ret = __put_user(x, to); \
-		else \
-			ret = -EFAULT;	\
-	} \
-	ret; \
+						sizeof(*ptr),		\
+						VHOST_ADDR_USED);	\
+		if (to != NULL)						\
+			ret = __put_user(x, to);			\
+		else							\
+			ret = -EFAULT;					\
+	}								\
+	ret;								\
 })
 
 static inline int vhost_put_avail_event(struct vhost_virtqueue *vq)
@@ -1252,22 +1253,21 @@ static inline int vhost_put_used_idx(struct vhost_virtqueue *vq)
 			      &vq->used->idx);
 }
 
-#define vhost_get_user(vq, x, ptr, type)		\
-({ \
-	int ret; \
-	if (!vq->iotlb) { \
-		ret = __get_user(x, ptr); \
-	} else { \
-		__typeof__(ptr) from = \
-			(__typeof__(ptr)) __vhost_get_user(vq, ptr, \
-							   sizeof(*ptr), \
-							   type); \
-		if (from != NULL) \
-			ret = __get_user(x, from); \
-		else \
-			ret = -EFAULT; \
-	} \
-	ret; \
+#define vhost_get_user(vq, x, ptr, type)				\
+({									\
+	int ret;							\
+	if (!vq->iotlb) {						\
+		ret = __get_user(x, ptr);				\
+	} else {							\
+		__typeof__(ptr) from =					\
+			(__typeof__(ptr)) __vhost_get_user(vq, ptr,	\
+						sizeof(*ptr), type);	\
+		if (from != NULL)					\
+			ret = __get_user(x, from);			\
+		else							\
+			ret = -EFAULT;					\
+	}								\
+	ret;								\
 })
 
 #define vhost_get_avail(vq, x, ptr) \
-- 
2.44.0

Re: [PATCH 3/4] vhost: Improve vhost_get_avail_head()

[kernel test robot]

Hi Gavin,

kernel test robot noticed the following build warnings:

[auto build test WARNING on mst-vhost/linux-next]
[also build test WARNING on linus/master v6.9-rc5 next-20240424]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Gavin-Shan/vhost-Drop-variable-last_avail_idx-in-vhost_get_vq_desc/20240423-112803
base:   https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git linux-next
patch link:    https://lore.kernel.org/r/20240423032407.262329-4-gshan%40redhat.com
patch subject: [PATCH 3/4] vhost: Improve vhost_get_avail_head()
config: i386-randconfig-141-20240426 (https://download.01.org/0day-ci/archive/20240426/202404260448.g7F06v7M-lkp@intel.com/config)
compiler: clang version 17.0.6 (https://github.com/llvm/llvm-project 6009708b4367171ccdbf4b5905cb6a803753fe18)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202404260448.g7F06v7M-lkp@intel.com/

smatch warnings:
drivers/vhost/vhost.c:2614 vhost_get_vq_desc() warn: unsigned 'head' is never less than zero.
drivers/vhost/vhost.c:2614 vhost_get_vq_desc() warn: error code type promoted to positive: 'head'

vim +/head +2614 drivers/vhost/vhost.c

  2581	
  2582	/* This looks in the virtqueue and for the first available buffer, and converts
  2583	 * it to an iovec for convenient access.  Since descriptors consist of some
  2584	 * number of output then some number of input descriptors, it's actually two
  2585	 * iovecs, but we pack them into one and note how many of each there were.
  2586	 *
  2587	 * This function returns the descriptor number found, or vq->num (which is
  2588	 * never a valid descriptor number) if none was found.  A negative code is
  2589	 * returned on error. */
  2590	int vhost_get_vq_desc(struct vhost_virtqueue *vq,
  2591			      struct iovec iov[], unsigned int iov_size,
  2592			      unsigned int *out_num, unsigned int *in_num,
  2593			      struct vhost_log *log, unsigned int *log_num)
  2594	{
  2595		struct vring_desc desc;
  2596		unsigned int i, head, found = 0;
  2597		int ret, access;
  2598	
  2599		if (vq->avail_idx == vq->last_avail_idx) {
  2600			ret = vhost_get_avail_idx(vq);
  2601			if (unlikely(ret))
  2602				return ret;
  2603	
  2604			/* If there's nothing new since last we looked, return
  2605			 * invalid.
  2606			 */
  2607			if (vq->avail_idx == vq->last_avail_idx)
  2608				return vq->num;
  2609		}
  2610	
  2611		/* Grab the next descriptor number they're advertising, and increment
  2612		 * the index we've seen. */
  2613		head = vhost_get_avail_head(vq);
> 2614		if (unlikely(head < 0))
  2615			return head;
  2616	
  2617		/* When we start there are none of either input nor output. */
  2618		*out_num = *in_num = 0;
  2619		if (unlikely(log))
  2620			*log_num = 0;
  2621	
  2622		i = head;
  2623		do {
  2624			unsigned iov_count = *in_num + *out_num;
  2625			if (unlikely(i >= vq->num)) {
  2626				vq_err(vq, "Desc index is %u > %u, head = %u",
  2627				       i, vq->num, head);
  2628				return -EINVAL;
  2629			}
  2630			if (unlikely(++found > vq->num)) {
  2631				vq_err(vq, "Loop detected: last one at %u "
  2632				       "vq size %u head %u\n",
  2633				       i, vq->num, head);
  2634				return -EINVAL;
  2635			}
  2636			ret = vhost_get_desc(vq, &desc, i);
  2637			if (unlikely(ret)) {
  2638				vq_err(vq, "Failed to get descriptor: idx %d addr %p\n",
  2639				       i, vq->desc + i);
  2640				return -EFAULT;
  2641			}
  2642			if (desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_INDIRECT)) {
  2643				ret = get_indirect(vq, iov, iov_size,
  2644						   out_num, in_num,
  2645						   log, log_num, &desc);
  2646				if (unlikely(ret < 0)) {
  2647					if (ret != -EAGAIN)
  2648						vq_err(vq, "Failure detected "
  2649							"in indirect descriptor at idx %d\n", i);
  2650					return ret;
  2651				}
  2652				continue;
  2653			}
  2654	
  2655			if (desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_WRITE))
  2656				access = VHOST_ACCESS_WO;
  2657			else
  2658				access = VHOST_ACCESS_RO;
  2659			ret = translate_desc(vq, vhost64_to_cpu(vq, desc.addr),
  2660					     vhost32_to_cpu(vq, desc.len), iov + iov_count,
  2661					     iov_size - iov_count, access);
  2662			if (unlikely(ret < 0)) {
  2663				if (ret != -EAGAIN)
  2664					vq_err(vq, "Translation failure %d descriptor idx %d\n",
  2665						ret, i);
  2666				return ret;
  2667			}
  2668			if (access == VHOST_ACCESS_WO) {
  2669				/* If this is an input descriptor,
  2670				 * increment that count. */
  2671				*in_num += ret;
  2672				if (unlikely(log && ret)) {
  2673					log[*log_num].addr = vhost64_to_cpu(vq, desc.addr);
  2674					log[*log_num].len = vhost32_to_cpu(vq, desc.len);
  2675					++*log_num;
  2676				}
  2677			} else {
  2678				/* If it's an output descriptor, they're all supposed
  2679				 * to come before any input descriptors. */
  2680				if (unlikely(*in_num)) {
  2681					vq_err(vq, "Descriptor has out after in: "
  2682					       "idx %d\n", i);
  2683					return -EINVAL;
  2684				}
  2685				*out_num += ret;
  2686			}
  2687		} while ((i = next_desc(vq, &desc)) != -1);
  2688	
  2689		/* On success, increment avail index. */
  2690		vq->last_avail_idx++;
  2691	
  2692		/* Assume notifications from guest are disabled at this point,
  2693		 * if they aren't we would need to update avail_event index. */
  2694		BUG_ON(!(vq->used_flags & VRING_USED_F_NO_NOTIFY));
  2695		return head;
  2696	}
  2697	EXPORT_SYMBOL_GPL(vhost_get_vq_desc);
  2698	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH 3/4] vhost: Improve vhost_get_avail_head()

[Gavin Shan]

On 4/26/24 06:42, kernel test robot wrote:> kernel test robot noticed the following build warnings:
> 
> [auto build test WARNING on mst-vhost/linux-next]
> [also build test WARNING on linus/master v6.9-rc5 next-20240424]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch#_base_tree_information]
> 
> url:    https://github.com/intel-lab-lkp/linux/commits/Gavin-Shan/vhost-Drop-variable-last_avail_idx-in-vhost_get_vq_desc/20240423-112803
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/mst/vhost.git linux-next
> patch link:    https://lore.kernel.org/r/20240423032407.262329-4-gshan%40redhat.com
> patch subject: [PATCH 3/4] vhost: Improve vhost_get_avail_head()
> config: i386-randconfig-141-20240426 (https://download.01.org/0day-ci/archive/20240426/202404260448.g7F06v7M-lkp@intel.com/config)
> compiler: clang version 17.0.6 (https://github.com/llvm/llvm-project 6009708b4367171ccdbf4b5905cb6a803753fe18)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202404260448.g7F06v7M-lkp@intel.com/
> 
> smatch warnings:
> drivers/vhost/vhost.c:2614 vhost_get_vq_desc() warn: unsigned 'head' is never less than zero.
> drivers/vhost/vhost.c:2614 vhost_get_vq_desc() warn: error code type promoted to positive: 'head'
> 
> vim +/head +2614 drivers/vhost/vhost.c
> 
>    2581	
>    2582	/* This looks in the virtqueue and for the first available buffer, and converts
>    2583	 * it to an iovec for convenient access.  Since descriptors consist of some
>    2584	 * number of output then some number of input descriptors, it's actually two
>    2585	 * iovecs, but we pack them into one and note how many of each there were.
>    2586	 *
>    2587	 * This function returns the descriptor number found, or vq->num (which is
>    2588	 * never a valid descriptor number) if none was found.  A negative code is
>    2589	 * returned on error. */
>    2590	int vhost_get_vq_desc(struct vhost_virtqueue *vq,
>    2591			      struct iovec iov[], unsigned int iov_size,
>    2592			      unsigned int *out_num, unsigned int *in_num,
>    2593			      struct vhost_log *log, unsigned int *log_num)
>    2594	{
>    2595		struct vring_desc desc;
>    2596		unsigned int i, head, found = 0;
>    2597		int ret, access;
>    2598	
>    2599		if (vq->avail_idx == vq->last_avail_idx) {
>    2600			ret = vhost_get_avail_idx(vq);
>    2601			if (unlikely(ret))
>    2602				return ret;
>    2603	
>    2604			/* If there's nothing new since last we looked, return
>    2605			 * invalid.
>    2606			 */
>    2607			if (vq->avail_idx == vq->last_avail_idx)
>    2608				return vq->num;
>    2609		}
>    2610	
>    2611		/* Grab the next descriptor number they're advertising, and increment
>    2612		 * the index we've seen. */
>    2613		head = vhost_get_avail_head(vq);
>>   2614		if (unlikely(head < 0))
>    2615			return head;

Thanks for the report. @head needs to be 'int' instead of 'unsigned int'
so that it can hold the error number from vhost_get_avail_head(). I would
give it more time to see if there are other review comments before I revise
it to fix it up.

Thanks,
Gavin

Re: [PATCH 0/4] vhost: Cleanup

[Michael S. Tsirkin]

On Tue, Apr 23, 2024 at 01:24:03PM +1000, Gavin Shan wrote:
> This is suggested by Michael S. Tsirkin according to [1] and the goal
> is to apply smp_rmb() inside vhost_get_avail_idx() if needed. With it,
> the caller of the function needn't to worry about memory barriers. Since
> we're here, other cleanups are also applied.


Gavin I suggested another approach.
1. Start with the patch I sent (vhost: order avail ring reads after
   index updates) just do a diff against latest.
   simplify error handling a bit.
2. Do any other cleanups on top.

> [1] https://lore.kernel.org/virtualization/20240327075940-mutt-send-email-mst@kernel.org/
> 
> PATCH[1] drops the local variable @last_avail_idx since it's equivalent
>          to vq->last_avail_idx
> PATCH[2] improves vhost_get_avail_idx() so that smp_rmb() is applied if
>          needed. Besides, the sanity checks on the retrieved available
>          queue index are also squeezed to vhost_get_avail_idx()
> PATCH[3] improves vhost_get_avail_head(), similar to what we're doing
>          for vhost_get_avail_idx(), so that the relevant sanity checks
>          on the head are squeezed to vhost_get_avail_head()
> PATCH[4] Reformat vhost_{get, put}_user() by using tab instead of space
>          as the terminator for each line
> 
> Gavin Shan (4):
>   vhost: Drop variable last_avail_idx in vhost_get_vq_desc()
>   vhost: Improve vhost_get_avail_idx() with smp_rmb()
>   vhost: Improve vhost_get_avail_head()
>   vhost: Reformat vhost_{get, put}_user()
> 
>  drivers/vhost/vhost.c | 199 +++++++++++++++++++-----------------------
>  1 file changed, 88 insertions(+), 111 deletions(-)
> 
> -- 
> 2.44.0

Re: [PATCH 0/4] vhost: Cleanup

[Gavin Shan]

On 4/29/24 17:02, Michael S. Tsirkin wrote:
> On Tue, Apr 23, 2024 at 01:24:03PM +1000, Gavin Shan wrote:
>> This is suggested by Michael S. Tsirkin according to [1] and the goal
>> is to apply smp_rmb() inside vhost_get_avail_idx() if needed. With it,
>> the caller of the function needn't to worry about memory barriers. Since
>> we're here, other cleanups are also applied.
> 
> 
> Gavin I suggested another approach.
> 1. Start with the patch I sent (vhost: order avail ring reads after
>     index updates) just do a diff against latest.
>     simplify error handling a bit.
> 2. Do any other cleanups on top.
> 

My apologies, Michael. I didn't see your patch until now [1]

   [1] https://lore.kernel.org/virtualization/20240327155750-mutt-send-email-mst@kernel.org/

v2 was sent with your changes integrated and other cleanup are applied on
top of it. Please take a look when you getting a chance.

   v2: https://lore.kernel.org/virtualization/20240429101400.617007-1-gshan@redhat.com/T/#t

Thanks,
Gavin