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Re: [RFC PATCH] vhost_net: should not use max_queue_pairs for non-mq gue
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From: |
Jason Wang |
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Subject: |
Re: [RFC PATCH] vhost_net: should not use max_queue_pairs for non-mq guest |
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Date: |
Tue, 22 Mar 2022 11:47:48 +0800 |
On Sat, Mar 19, 2022 at 12:14 PM Si-Wei Liu <si-wei.liu@oracle.com> wrote:
>
> With MQ enabled vdpa device and non-MQ supporting guest e.g.
> booting vdpa with mq=on over OVMF of single vqp, it's easy
> to hit assert failure as the following:
>
> ../hw/virtio/vhost-vdpa.c:560: vhost_vdpa_get_vq_index: Assertion `idx >=
> dev->vq_index && idx < dev->vq_index + dev->nvqs' failed.
>
> 0 0x00007f8ce3ff3387 in raise () at /lib64/libc.so.6
> 1 0x00007f8ce3ff4a78 in abort () at /lib64/libc.so.6
> 2 0x00007f8ce3fec1a6 in __assert_fail_base () at /lib64/libc.so.6
> 3 0x00007f8ce3fec252 in () at /lib64/libc.so.6
> 4 0x0000558f52d79421 in vhost_vdpa_get_vq_index (dev=<optimized out>,
> idx=<optimized out>) at ../hw/virtio/vhost-vdpa.c:563
> 5 0x0000558f52d79421 in vhost_vdpa_get_vq_index (dev=<optimized out>,
> idx=<optimized out>) at ../hw/virtio/vhost-vdpa.c:558
> 6 0x0000558f52d7329a in vhost_virtqueue_mask (hdev=0x558f55c01800,
> vdev=0x558f568f91f0, n=2, mask=<optimized out>) at ../hw/virtio/vhost.c:1557
> 7 0x0000558f52c6b89a in virtio_pci_set_guest_notifier
> (d=d@entry=0x558f568f0f60, n=n@entry=2, assign=assign@entry=true,
> with_irqfd=with_irqfd@entry=false)
> at ../hw/virtio/virtio-pci.c:974
> 8 0x0000558f52c6c0d8 in virtio_pci_set_guest_notifiers (d=0x558f568f0f60,
> nvqs=3, assign=true) at ../hw/virtio/virtio-pci.c:1019
> 9 0x0000558f52bf091d in vhost_net_start (dev=dev@entry=0x558f568f91f0,
> ncs=0x558f56937cd0, data_queue_pairs=data_queue_pairs@entry=1,
> cvq=cvq@entry=1)
> at ../hw/net/vhost_net.c:361
> 10 0x0000558f52d4e5e7 in virtio_net_set_status (status=<optimized out>,
> n=0x558f568f91f0) at ../hw/net/virtio-net.c:289
> 11 0x0000558f52d4e5e7 in virtio_net_set_status (vdev=0x558f568f91f0,
> status=15 '\017') at ../hw/net/virtio-net.c:370
> 12 0x0000558f52d6c4b2 in virtio_set_status (vdev=vdev@entry=0x558f568f91f0,
> val=val@entry=15 '\017') at ../hw/virtio/virtio.c:1945
> 13 0x0000558f52c69eff in virtio_pci_common_write (opaque=0x558f568f0f60,
> addr=<optimized out>, val=<optimized out>, size=<optimized out>) at
> ../hw/virtio/virtio-pci.c:1292
> 14 0x0000558f52d15d6e in memory_region_write_accessor (mr=0x558f568f19d0,
> addr=20, value=<optimized out>, size=1, shift=<optimized out>,
> mask=<optimized out>, attrs=...)
> at ../softmmu/memory.c:492
> 15 0x0000558f52d127de in access_with_adjusted_size (addr=addr@entry=20,
> value=value@entry=0x7f8cdbffe748, size=size@entry=1,
> access_size_min=<optimized out>, access_size_max=<optimized out>,
> access_fn=0x558f52d15cf0 <memory_region_write_accessor>, mr=0x558f568f19d0,
> attrs=...) at ../softmmu/memory.c:554
> 16 0x0000558f52d157ef in memory_region_dispatch_write
> (mr=mr@entry=0x558f568f19d0, addr=20, data=<optimized out>, op=<optimized
> out>, attrs=attrs@entry=...)
> at ../softmmu/memory.c:1504
> 17 0x0000558f52d078e7 in flatview_write_continue (fv=fv@entry=0x7f8accbc3b90,
> addr=addr@entry=103079215124, attrs=..., ptr=ptr@entry=0x7f8ce6300028,
> len=len@entry=1, addr1=<optimized out>, l=<optimized out>, mr=0x558f568f19d0)
> at /home/opc/qemu-upstream/include/qemu/host-utils.h:165
> 18 0x0000558f52d07b06 in flatview_write (fv=0x7f8accbc3b90,
> addr=103079215124, attrs=..., buf=0x7f8ce6300028, len=1) at
> ../softmmu/physmem.c:2822
> 19 0x0000558f52d0b36b in address_space_write (as=<optimized out>,
> addr=<optimized out>, attrs=..., buf=buf@entry=0x7f8ce6300028, len=<optimized
> out>)
> at ../softmmu/physmem.c:2914
> 20 0x0000558f52d0b3da in address_space_rw (as=<optimized out>,
> addr=<optimized out>, attrs=...,
> attrs@entry=..., buf=buf@entry=0x7f8ce6300028, len=<optimized out>,
> is_write=<optimized out>) at ../softmmu/physmem.c:2924
> 21 0x0000558f52dced09 in kvm_cpu_exec (cpu=cpu@entry=0x558f55c2da60) at
> ../accel/kvm/kvm-all.c:2903
> 22 0x0000558f52dcfabd in kvm_vcpu_thread_fn (arg=arg@entry=0x558f55c2da60) at
> ../accel/kvm/kvm-accel-ops.c:49
> 23 0x0000558f52f9f04a in qemu_thread_start (args=<optimized out>) at
> ../util/qemu-thread-posix.c:556
> 24 0x00007f8ce4392ea5 in start_thread () at /lib64/libpthread.so.0
> 25 0x00007f8ce40bb9fd in clone () at /lib64/libc.so.6
>
> The cause for the assert failure is due to that the vhost_dev index
> for the ctrl vq was not aligned with actual one in use by the guest.
> Upon multiqueue feature negotiation in virtio_net_set_multiqueue(),
> if guest doesn't support multiqueue, the guest vq layout would shrink
> to single queue pair of 3 vqs in total (rx, tx and ctrl). This results
> in ctrl_vq taking a different vhost_dev group index than the default
> n->max_queue_pairs, the latter of which is only valid for multiqueue
> guest. While on those additional vqs not exposed to the guest,
> vhost_net_set_vq_index() never populated vq_index properly, hence
> getting the assert failure.
>
> A possible fix is to pick the correct vhost_dev group for the control
> vq according to this table [*]:
>
> vdpa tool / QEMU arg / guest config / ctrl_vq group index
> ----------------------------------------------------------------
> max_vqp 8 / mq=on / mq=off (UEFI) => data_queue_pairs
> max_vqp 8 / mq=on / mq=on (Linux) => n->max_queue_pairs(>1)
> max_vqp 8 / mq=off / mq=on (Linux) => n->max_queue_pairs(=1)
>
> [*] Please see FIXME in the code for open question and discussion
>
> Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com>
> ---
> hw/net/vhost_net.c | 13 +++++++++----
> hw/virtio/vhost-vdpa.c | 25 ++++++++++++++++++++++++-
> 2 files changed, 33 insertions(+), 5 deletions(-)
>
> diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
> index 30379d2..9a4479b 100644
> --- a/hw/net/vhost_net.c
> +++ b/hw/net/vhost_net.c
> @@ -322,6 +322,7 @@ int vhost_net_start(VirtIODevice *dev, NetClientState
> *ncs,
> BusState *qbus = BUS(qdev_get_parent_bus(DEVICE(dev)));
> VirtioBusState *vbus = VIRTIO_BUS(qbus);
> VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(vbus);
> + bool mq = virtio_host_has_feature(dev, VIRTIO_NET_F_MQ);
> int total_notifiers = data_queue_pairs * 2 + cvq;
> VirtIONet *n = VIRTIO_NET(dev);
> int nvhosts = data_queue_pairs + cvq;
> @@ -343,7 +344,7 @@ int vhost_net_start(VirtIODevice *dev, NetClientState
> *ncs,
> if (i < data_queue_pairs) {
> peer = qemu_get_peer(ncs, i);
> } else { /* Control Virtqueue */
> - peer = qemu_get_peer(ncs, n->max_queue_pairs);
> + peer = qemu_get_peer(ncs, mq ? data_queue_pairs :
> n->max_queue_pairs);
> }
>
> net = get_vhost_net(peer);
> @@ -368,7 +369,7 @@ int vhost_net_start(VirtIODevice *dev, NetClientState
> *ncs,
> if (i < data_queue_pairs) {
> peer = qemu_get_peer(ncs, i);
> } else {
> - peer = qemu_get_peer(ncs, n->max_queue_pairs);
> + peer = qemu_get_peer(ncs, mq ? data_queue_pairs :
> n->max_queue_pairs);
> }
> r = vhost_net_start_one(get_vhost_net(peer), dev);
>
> @@ -390,7 +391,10 @@ int vhost_net_start(VirtIODevice *dev, NetClientState
> *ncs,
>
> err_start:
> while (--i >= 0) {
> - peer = qemu_get_peer(ncs , i);
> + if (mq)
> + peer = qemu_get_peer(ncs, i < data_queue_pairs ? i :
> data_queue_pairs);
> + else
> + peer = qemu_get_peer(ncs, i < data_queue_pairs ? i :
> n->max_queue_pairs);
> vhost_net_stop_one(get_vhost_net(peer), dev);
> }
> e = k->set_guest_notifiers(qbus->parent, total_notifiers, false);
> @@ -409,6 +413,7 @@ void vhost_net_stop(VirtIODevice *dev, NetClientState
> *ncs,
> VirtioBusState *vbus = VIRTIO_BUS(qbus);
> VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(vbus);
> VirtIONet *n = VIRTIO_NET(dev);
> + bool mq = virtio_host_has_feature(dev, VIRTIO_NET_F_MQ);
> NetClientState *peer;
> int total_notifiers = data_queue_pairs * 2 + cvq;
> int nvhosts = data_queue_pairs + cvq;
> @@ -418,7 +423,7 @@ void vhost_net_stop(VirtIODevice *dev, NetClientState
> *ncs,
> if (i < data_queue_pairs) {
> peer = qemu_get_peer(ncs, i);
> } else {
> - peer = qemu_get_peer(ncs, n->max_queue_pairs);
> + peer = qemu_get_peer(ncs, mq ? data_queue_pairs :
> n->max_queue_pairs);
> }
> vhost_net_stop_one(get_vhost_net(peer), dev);
> }
> diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> index 27ea706..623476e 100644
> --- a/hw/virtio/vhost-vdpa.c
> +++ b/hw/virtio/vhost-vdpa.c
> @@ -1097,7 +1097,30 @@ static int vhost_vdpa_dev_start(struct vhost_dev *dev,
> bool started)
> vhost_vdpa_host_notifiers_uninit(dev, dev->nvqs);
> }
>
> - if (dev->vq_index + dev->nvqs != dev->vq_index_end) {
> + /* FIXME the vhost_dev group for the control vq may have bogus nvqs=2
> + * value rather than nvqs=1. This can happen in case the guest doesn't
> + * support multiqueue, as a result of virtio_net_change_num_queue_pairs()
> + * destroying and rebuilding all the vqs, the guest index for control vq
> + * will no longer align with the host's. Currently net_init_vhost_vdpa()
> + * only initializes all vhost_dev's and net_clients once during
> + * net_client_init1() time, way earlier before multiqueue feature
> + * negotiation can kick in.
See below, it looks like the code doesn't find the correct vhost_dev.
> + *
> + * Discussion - some possible fixes so far I can think of:
> + *
> + * option 1: fix vhost_net->dev.nvqs and nc->is_datapath in place for
> + * vdpa's ctrl vq, or rebuild all vdpa's vhost_dev groups and the
> + * net_client array, in the virtio_net_set_multiqueue() path;
> + *
> + * option 2: fix vhost_dev->nvqs in place at vhost_vdpa_set_features()
> + * before coming down to vhost_vdpa_dev_start() (Q: nc->is_datapath
> + * seems only used in virtio_net_device_realize, is it relevant?);
Relevant but not directly related, for the vhost_dev where
nc->is_datapath is false, it will assume it is backed by a single
queue not a queue pair.
> + *
> + * option 3: use host queue index all along in vhost-vdpa ioctls instead
> + * of using guest vq index, so that vhost_net_start/stop() can remain
> + * as-is today
> + */
Note that the vq_index of each vhost_dev is assigned during
vhost_net_start() according to whether or not the MQ or CVQ is
negotiated in vhost_net_start()
for (i = 0; i < nvhosts; i++) {
if (i < data_queue_pairs) {
peer = qemu_get_peer(ncs, i);
} else { /* Control Virtqueue */
peer = qemu_get_peer(ncs, n->max_queue_pairs);
}
net = get_vhost_net(peer);
vhost_net_set_vq_index(net, i * 2, index_end);
It means some of the peers won't be used when MQ is not negotiated. So
it looks to me the evil came from virtio_net_get_notifier_mask().
Where it doesn't mask the correct vhost dev when the guest doesn't
support MQ but the host does. So we had option 4:
diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 2087516253..5e9ac019cd 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -3179,7 +3179,13 @@ static void
virtio_net_guest_notifier_mask(VirtIODevice *vdev, int idx,
bool mask)
{
VirtIONet *n = VIRTIO_NET(vdev);
- NetClientState *nc = qemu_get_subqueue(n->nic, vq2q(idx));
+ NetClientState *nc;
+
+ if (!virtio_vdev_has_feature(vdev, VIRTIO_NET_F_MQ) && idx == 2) {
+ nc = qemu_get_subqueue(n->nic, n->max_queue_pairs);
+ } else {
+ nc = qemu_get_subqueue(n->nic, vq2q(idx));
+ }
assert(n->vhost_started);
vhost_net_virtqueue_mask(get_vhost_net(nc->peer),
vdev, idx, mask);
Thanks
> + if (dev->vq_index + dev->nvqs < dev->vq_index_end) {
> return 0;
> }
>
> --
> 1.8.3.1
>