A smp_rmb() has been missed in vhost_enable_notify(), inspired by
Will Deacon <will@xxxxxxxxxx>. Otherwise, it's not ensured the
available ring entries pushed by guest can be observed by vhost
in time, leading to stale available ring entries fetched by vhost
in vhost_get_vq_desc(), as reported by Yihuang Yu on NVidia's
grace-hopper (ARM64) platform.
/home/gavin/sandbox/qemu.main/build/qemu-system-aarch64 \
-accel kvm -machine virt,gic-version=host -cpu host \
-smp maxcpus=1,cpus=1,sockets=1,clusters=1,cores=1,threads=1 \
-m 4096M,slots=16,maxmem=64G \
-object memory-backend-ram,id=mem0,size=4096M \
: \
-netdev tap,id=vnet0,vhost=true \
-device virtio-net-pci,bus=pcie.8,netdev=vnet0,mac=52:54:00:f1:26:b0
:
guest# netperf -H 10.26.1.81 -l 60 -C -c -t UDP_STREAM
virtio_net virtio0: output.0:id 100 is not a head!
Add the missed smp_rmb() in vhost_enable_notify(). Note that it
should be safe until vq->avail_idx is changed by commit d3bb267bbdcb
("vhost: cache avail index in vhost_enable_notify()").
Fixes: d3bb267bbdcb ("vhost: cache avail index in vhost_enable_notify()")
Cc: <stable@xxxxxxxxxx> # v5.18+
Reported-by: Yihuang Yu <yihyu@xxxxxxxxxx>
Signed-off-by: Gavin Shan <gshan@xxxxxxxxxx>
---
drivers/vhost/vhost.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 00445ab172b3..58f9d6a435f0 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2847,9 +2847,18 @@ bool vhost_enable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
&vq->avail->idx, r);
return false;
}
+
vq->avail_idx = vhost16_to_cpu(vq, avail_idx);
+ if (vq->avail_idx != vq->last_avail_idx) {
+ /* Similar to what's done in vhost_get_vq_desc(), we need
+ * to ensure the available ring entries have been exposed
+ * by guest.
+ */
+ smp_rmb();
+ return true;
+ }
- return vq->avail_idx != vq->last_avail_idx;
+ return false;
}
EXPORT_SYMBOL_GPL(vhost_enable_notify);
--
2.44.0
