The issue was reported by Yihuang Yu on NVidia's grace-hopper (ARM64) platform. The wrong head (available ring entry) is seen by the guest when running 'netperf' on the guest and running 'netserver' on another NVidia's grace-grace machine. /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=tap0,vhost=true \ -device virtio-net-pci,bus=pcie.8,netdev=tap0,mac=52:54:00:f1:26:b0 : guest# ifconfig eth0 | grep 'inet addr' inet addr:10.26.1.220 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! There is missed smp_rmb() in vhost_vq_avail_empty() and vhost_enable_notify(). Without smp_rmb(), vq->avail_idx is increased but the available ring entries aren't arriving to vhost side yet. So a stale available ring entry can be fetched in vhost_get_vq_desc(). Fix it by adding smp_rmb() in those two functions. Note that I need two patches so that they can be easily picked up by the stable kernel. With the changes, I'm unable to hit the issue again. Gavin Shan (2): vhost: Add smp_rmb() in vhost_vq_avail_empty() vhost: Add smp_rmb() in vhost_enable_notify() drivers/vhost/vhost.c | 22 ++++++++++++++++++++-- 1 file changed, 20 insertions(+), 2 deletions(-) -- 2.44.0
