Messages in this thread | | | Date | Thu, 28 Mar 2024 10:48:18 +0100 | From | Stefano Garzarella <> | Subject | Re: [PATCH v3 2/3] vhost: Add smp_rmb() in vhost_enable_notify() |
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On Thu, Mar 28, 2024 at 10:21:48AM +1000, Gavin Shan wrote: >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 d3bb267bbdcb >("vhost: cache avail index in vhost_enable_notify()"). > >Fixes: d3bb267bbdcb ("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> >--- > drivers/vhost/vhost.c | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-)
Thanks for fixing this!
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
> >diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c >index 29df65b2ebf2..32686c79c41d 100644 >--- a/drivers/vhost/vhost.c >+++ b/drivers/vhost/vhost.c >@@ -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); >+ 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 vq->avail_idx != vq->last_avail_idx; >+ return false; > } > EXPORT_SYMBOL_GPL(vhost_enable_notify); > >-- >2.44.0 >
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