Re: [PATCH] vhost-user: Check for iotlb callback in iotlb_miss

[Jason Wang]

On 2021/1/28 下午5:37, Eugenio Perez Martin wrote:
> Hi Jason.
>
> On Thu, Jan 28, 2021 at 3:32 AM Jason Wang <jasowang@redhat.com> wrote:
> > On 2021/1/28 上午4:44, Eugenio Pérez wrote:
> > > Not registering this can lead to vhost_backend_handle_iotlb_msg and
> > > vhost_device_iotlb_miss if backend issue a miss after qemu vhost device
> > > stop.
> > >
> > > This causes a try to access dev->vdev->dma_as with vdev == NULL.
> >
> > Hi Eugenio:
> >
> > What condition can we get this? Did you mean we receive IOTLB_MISS
> > before vhost_dev_start()?
> In the VM reboot case, yes, between vhost_dev_stop() and
> vhost_dev_start(). But I can reproduce the bug in VM shutdown too,
> with no vhost_dev_start expected.
>
> I didn't try to send IOTLB_MISS before starting vhost_dev, but this
> patch should solve that problem too.
>
> I think we can get this with whatever malicious/buggy vhost-user
> backend sending unexpected iotlb misses, but I didn't test so deeply.


I see.


> > If yes, it looks to me a bug somewhere else.
> Where should I look for it?


So I winder whether or not we can simply ignore IOTLB message if vhost 
device is not started.

Thanks


> Thanks!
>
> > Thanks
> >
> >
> > > Reproduced rebooting a guest with testpmd in txonly forward mode.
> > >    #0  0x0000559ffff94394 in vhost_device_iotlb_miss (
> > >        dev=dev@entry=0x55a0012f6680, iova=10245279744, write=1)
> > >        at ../hw/virtio/vhost.c:1013
> > >    #1  0x0000559ffff9ac31 in vhost_backend_handle_iotlb_msg (
> > >        imsg=0x7ffddcfd32c0, dev=0x55a0012f6680)
> > >        at ../hw/virtio/vhost-backend.c:411
> > >    #2  vhost_backend_handle_iotlb_msg (dev=dev@entry=0x55a0012f6680,
> > >        imsg=imsg@entry=0x7ffddcfd32c0)
> > >        at ../hw/virtio/vhost-backend.c:404
> > >    #3  0x0000559fffeded7b in slave_read (opaque=0x55a0012f6680)
> > >        at ../hw/virtio/vhost-user.c:1464
> > >    #4  0x000055a0000c541b in aio_dispatch_handler (
> > >        ctx=ctx@entry=0x55a0010a2120, node=0x55a0012d9e00)
> > >        at ../util/aio-posix.c:329
> > >
> > > Fixes: 6dcdd06e3b ("spec/vhost-user spec: Add IOMMU support")
> > > Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> > > ---
> > >    hw/virtio/vhost-user.c | 10 ++++++++--
> > >    1 file changed, 8 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> > > index 2fdd5daf74..a49b2229fb 100644
> > > --- a/hw/virtio/vhost-user.c
> > > +++ b/hw/virtio/vhost-user.c
> > > @@ -238,6 +238,7 @@ struct vhost_user {
> > >        /* Shared between vhost devs of the same virtio device */
> > >        VhostUserState *user;
> > >        int slave_fd;
> > > +    bool iotlb_enabled;
> > >        NotifierWithReturn postcopy_notifier;
> > >        struct PostCopyFD  postcopy_fd;
> > >        uint64_t           postcopy_client_bases[VHOST_USER_MAX_RAM_SLOTS];
> > > @@ -1461,7 +1462,11 @@ static void slave_read(void *opaque)
> > >
> > >        switch (hdr.request) {
> > >        case VHOST_USER_SLAVE_IOTLB_MSG:
> > > -        ret = vhost_backend_handle_iotlb_msg(dev, &payload.iotlb);
> > > +        if (likely(u->iotlb_enabled)) {
> > > +            ret = vhost_backend_handle_iotlb_msg(dev, &payload.iotlb);
> > > +        } else {
> > > +            ret = -EFAULT;
> > > +        }
> > >            break;
> > >        case VHOST_USER_SLAVE_CONFIG_CHANGE_MSG :
> > >            ret = vhost_user_slave_handle_config_change(dev);
> > > @@ -2044,7 +2049,8 @@ static int vhost_user_send_device_iotlb_msg(struct 
> > > vhost_dev *dev,
> > >
> > >    static void vhost_user_set_iotlb_callback(struct vhost_dev *dev, int enabled)
> > >    {
> > > -    /* No-op as the receive channel is not dedicated to IOTLB messages. */
> > > +    struct vhost_user *u = dev->opaque;
> > > +    u->iotlb_enabled = enabled;
> > >    }
> > >
> > >    static int vhost_user_get_config(struct vhost_dev *dev, uint8_t *config,