This is a note to let you know that I've just added the patch titled
vhost: Add smp_rmb() in vhost_vq_avail_empty()
to the 6.8-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
vhost-add-smp_rmb-in-vhost_vq_avail_empty.patch
and it can be found in the queue-6.8 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 22e1992cf7b034db5325660e98c41ca5afa5f519 Mon Sep 17 00:00:00 2001
From: Gavin Shan <gshan@xxxxxxxxxx>
Date: Thu, 28 Mar 2024 10:21:47 +1000
Subject: vhost: Add smp_rmb() in vhost_vq_avail_empty()
From: Gavin Shan <gshan@xxxxxxxxxx>
commit 22e1992cf7b034db5325660e98c41ca5afa5f519 upstream.
A smp_rmb() has been missed in vhost_vq_avail_empty(), spotted 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_vq_avail_empty(). When tx_can_batch()
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
275bf960ac697 ("vhost: better detection of available buffers").
Fixes: 275bf960ac69 ("vhost: better detection of available buffers")
Cc: <stable@xxxxxxxxxx> # v4.11+
Reported-by: Yihuang Yu <yihyu@xxxxxxxxxx>
Suggested-by: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Gavin Shan <gshan@xxxxxxxxxx>
Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
Message-Id: <20240328002149.1141302-2-gshan@xxxxxxxxxx>
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Reviewed-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/vhost/vhost.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2799,9 +2799,19 @@ bool vhost_vq_avail_empty(struct vhost_d
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 vq->avail_idx == vq->last_avail_idx;
+ return true;
}
EXPORT_SYMBOL_GPL(vhost_vq_avail_empty);
Patches currently in stable-queue which might be from gshan@xxxxxxxxxx are
queue-6.8/arm64-tlb-fix-tlbi-range-operand.patch
queue-6.8/vhost-add-smp_rmb-in-vhost_enable_notify.patch
queue-6.8/vhost-add-smp_rmb-in-vhost_vq_avail_empty.patch
