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

[Eugenio Perez Martin <eperezma@redhat.com>]

On Fri, Jan 29, 2021 at 4:29 AM Jason Wang <jasowang@redhat.com> wrote:
>
>
> 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.
>

Do you mean like an early return in vhost_device_iotlb_miss? That was
my first first option, but this seems cleaner to me. I'm ok with both
options.

Or do you mean not to return -EFAULT but 0 if !u->iotlb_enabled ?

Thanks!

> 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,
>