Re: [PATCH 1/7] virtio-net: align ctrl_vq index for non-mq guest for vhost_vdpa

[Jason Wang]

On Wed, Mar 30, 2022 at 11:48 PM Si-Wei Liu <si-wei.liu@oracle.com> wrote:
>
>
>
> On 3/30/2022 2:00 AM, Jason Wang wrote:
> > On Wed, Mar 30, 2022 at 2:33 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, below assert
> >> failure is seen:
> >>
> >> ../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 a single queue pair, consisting of 3 vqs in total (rx, tx and ctrl).
> >> This results in ctrl_vq taking a different vhost_dev group index than
> >> the default. We can map vq to the correct vhost_dev group by checking
> >> if MQ is supported by guest and successfully negotiated. Since the
> >> MQ feature is only present along with CTRL_VQ, we make sure the index
> >> 2 is only meant for the control vq while MQ is not supported by guest.
> >>
> >> Be noted if QEMU or guest doesn't support control vq, there's no bother
> >> exposing vhost_dev and guest notifier for the control vq. Since
> >> vhost_net_start/stop implies DRIVER_OK is set in device status, feature
> >> negotiation should be completed when reaching virtio_net_vhost_status().
> >>
> >> Fixes: 22288fe ("virtio-net: vhost control virtqueue support")
> >> Suggested-by: Jason Wang <jasowang@redhat.com>
> >> Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com>
> >> ---
> >>   hw/net/virtio-net.c | 19 ++++++++++++++++---
> >>   1 file changed, 16 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> >> index 1067e72..484b215 100644
> >> --- a/hw/net/virtio-net.c
> >> +++ b/hw/net/virtio-net.c
> >> @@ -245,7 +245,8 @@ static void virtio_net_vhost_status(VirtIONet *n, 
> >> uint8_t status)
> >>       VirtIODevice *vdev = VIRTIO_DEVICE(n);
> >>       NetClientState *nc = qemu_get_queue(n->nic);
> >>       int queue_pairs = n->multiqueue ? n->max_queue_pairs : 1;
> >> -    int cvq = n->max_ncs - n->max_queue_pairs;
> >> +    int cvq = virtio_vdev_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ) ?
> >> +              n->max_ncs - n->max_queue_pairs : 0;
> > Let's use a separate patch for this.
> Yes, I can do that. Then the new patch will become a requisite for this
> patch.
>
> >
> >>       if (!get_vhost_net(nc->peer)) {
> >>           return;
> >> @@ -3170,8 +3171,14 @@ static NetClientInfo net_virtio_info = {
> >>   static bool virtio_net_guest_notifier_pending(VirtIODevice *vdev, int 
> >> idx)
> >>   {
> >>       VirtIONet *n = VIRTIO_NET(vdev);
> >> -    NetClientState *nc = qemu_get_subqueue(n->nic, vq2q(idx));
> >> +    NetClientState *nc;
> >>       assert(n->vhost_started);
> >> +    if (!virtio_vdev_has_feature(vdev, VIRTIO_NET_F_MQ) && idx == 2) {
> >> +        assert(virtio_vdev_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ));
> > This assert seems guest trigger-able. If yes, I would remove this or
> > replace it with log_guest_error.
> This assert actually is relevant to the cvq change in
> virtio_net_vhost_status(). Since the same check on VIRTIO_NET_F_CTRL_VQ
> has been done earlier, it is assured that CTRL_VQ is negotiated when
> getting here.
> Noted the vhost_started is asserted in the same function, which in turn
> implies DRIVER_OK is set meaning feature negotiation is complete. I
> can't easily think of a scenario which guest may inadvertently or
> purposely trigger the assert?

So the code can be triggered like e.g unmasking:

virtio_pci_vq_vector_unmask()
        k->guest_notifier_pending()

Thanks


>
> -Siwei
>
> >
> >> +        nc = qemu_get_subqueue(n->nic, n->max_queue_pairs);
> >> +    } else {
> >> +        nc = qemu_get_subqueue(n->nic, vq2q(idx));
> >> +    }
> >>       return vhost_net_virtqueue_pending(get_vhost_net(nc->peer), idx);
> >>   }
> >>
> >> @@ -3179,8 +3186,14 @@ 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;
> >>       assert(n->vhost_started);
> >> +    if (!virtio_vdev_has_feature(vdev, VIRTIO_NET_F_MQ) && idx == 2) {
> >> +        assert(virtio_vdev_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ));
> > And this.
> >
> > Thanks
> >
> >
> >> +        nc = qemu_get_subqueue(n->nic, n->max_queue_pairs);
> >> +    } else {
> >> +        nc = qemu_get_subqueue(n->nic, vq2q(idx));
> >> +    }
> >>       vhost_net_virtqueue_mask(get_vhost_net(nc->peer),
> >>                                vdev, idx, mask);
> >>   }
> >> --
> >> 1.8.3.1
> >>
>