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Message-ID: <20240429101400.617007-2-gshan@redhat.com>
Date: Mon, 29 Apr 2024 20:13:57 +1000
From: Gavin Shan <gshan@...hat.com>
To: virtualization@...ts.linux.dev
Cc: linux-kernel@...r.kernel.org,
mst@...hat.com,
jasowang@...hat.com,
shan.gavin@...il.com
Subject: [PATCH v2 1/4] vhost: Improve vhost_get_avail_idx() with smp_rmb()
From: "Michael S. Tsirkin" <mst@...hat.com>
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.
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
[gshan: repainted vhost_get_avail_idx()]
Reviewed-by: Gavin Shan <gshan@...hat.com>
Acked-by: Will Deacon <will@...nel.org>
---
drivers/vhost/vhost.c | 106 +++++++++++++++++-------------------------
1 file changed, 42 insertions(+), 64 deletions(-)
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 8995730ce0bf..7aa623117aab 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1290,10 +1290,36 @@ 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 idx;
+ int r;
+
+ r = vhost_get_avail(vq, idx, &vq->avail->idx);
+ if (unlikely(r < 0)) {
+ vq_err(vq, "Failed to access available index at %p (%d)\n",
+ &vq->avail->idx, r);
+ return r;
+ }
+
+ /* Check it isn't doing very strange thing with available indexes */
+ vq->avail_idx = vhost16_to_cpu(vq, idx);
+ if (unlikely((u16)(vq->avail_idx - vq->last_avail_idx) > vq->num)) {
+ vq_err(vq, "Invalid available index change from %u to %u",
+ vq->last_avail_idx, vq->avail_idx);
+ return -EINVAL;
+ }
+
+ /* We're done if there is nothing new */
+ if (vq->avail_idx == vq->last_avail_idx)
+ return 0;
+
+ /*
+ * We updated vq->avail_idx so we need a memory barrier between
+ * the index read above and the caller reading avail ring entries.
+ */
+ smp_rmb();
+ return 1;
}
static inline int vhost_get_avail_head(struct vhost_virtqueue *vq,
@@ -2498,38 +2524,17 @@ 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;
+ u16 last_avail_idx = vq->last_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 avail index from %u to %u",
- last_avail_idx, vq->avail_idx);
- return -EFAULT;
- }
+ ret = vhost_get_avail_idx(vq);
+ if (unlikely(ret < 0))
+ return ret;
- /* If there's nothing new since last we looked, return
- * invalid.
- */
- if (vq->avail_idx == last_avail_idx)
+ if (!ret)
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
@@ -2790,35 +2795,20 @@ 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();
- return false;
- }
-
- return true;
+ /* Treat error as non-empty here */
+ r = vhost_get_avail_idx(vq);
+ return r == 0;
}
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))
@@ -2842,25 +2832,13 @@ 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);
- 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;
- }
+ /* Treat error as empty here */
+ r = vhost_get_avail_idx(vq);
+ if (unlikely(r < 0))
+ return false;
- return false;
+ return r;
}
EXPORT_SYMBOL_GPL(vhost_enable_notify);
--
2.44.0
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