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vhost: Add smp_rmb() in vhost_enable_notify() 

A smp_rmb() has been missed in vhost_enable_notify(), inspired by
Will. 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(). When it returns true,
it means there's still pending tx buffers. Since it might read indices,
so it still can bypass the smp_rmb() in vhost_get_vq_desc(). Note that
it should be safe until vq->avail_idx is changed by commit d3bb267bbd
("vhost: cache avail index in vhost_enable_notify()").

Fixes: d3bb267bbd ("vhost: cache avail index in vhost_enable_notify()")
Cc: <stable@kernel.org> # v5.18+
Reported-by: Yihuang Yu <yihyu@redhat.com>
Suggested-by: Will Deacon <will@kernel.org>
Signed-off-by: Gavin Shan <gshan@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20240328002149.1141302-3-gshan@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
This commit is contained in:
Gavin Shan 2024-03-28 10:21:48 +10:00 committed by Michael S. Tsirkin
parent 22e1992cf7
commit df9ace7647
1 changed files with 12 additions and 2 deletions
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14
drivers/vhost/vhost.c
View File

@ -2848,9 +2848,19 @@ 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);
return vq->avail_idx != vq->last_avail_idx;
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;
}
EXPORT_SYMBOL_GPL(vhost_enable_notify);