[dpdk-dev,1/4] vhost: prevent features to be changed while device is running

  As section 2.2 of the Virtio spec states about features
negotiation:
"During device initialization, the driver reads this and tells
the device the subset that it accepts. The only way to
renegotiate is to reset the device."

This patch implements a check to prevent illegal features change
while the device is running.

One exception is the VHOST_F_LOG_ALL feature bit, which is enabled
when live-migration is initiated. But this feature is not negotiated
with the Virtio driver, but directly with the Vhost master.

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
---
 lib/librte_vhost/vhost_user.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)
  

On Mon, Dec 4, 2017 at 3:08 PM, Maxime Coquelin
<maxime.coquelin@redhat.com> wrote:
> As section 2.2 of the Virtio spec states about features
> negotiation:
> "During device initialization, the driver reads this and tells
> the device the subset that it accepts. The only way to
> renegotiate is to reset the device."
>
> This patch implements a check to prevent illegal features change
> while the device is running.
>
> One exception is the VHOST_F_LOG_ALL feature bit, which is enabled
> when live-migration is initiated. But this feature is not negotiated
> with the Virtio driver, but directly with the Vhost master.
>
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> ---
>  lib/librte_vhost/vhost_user.c | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
> index f4c7ce462..f51055ab2 100644
> --- a/lib/librte_vhost/vhost_user.c
> +++ b/lib/librte_vhost/vhost_user.c
> @@ -183,7 +183,22 @@ vhost_user_set_features(struct virtio_net *dev, uint64_t features)
>                 return -1;
>         }
>
> -       if ((dev->flags & VIRTIO_DEV_RUNNING) && dev->features != features) {
> +       if (dev->features == features)
> +               return 0;
> +
> +       if (dev->flags & VIRTIO_DEV_RUNNING) {
> +               /*
> +                * Error out if master tries to change features while device is
> +                * in running state. The exception being VHOST_F_LOG_ALL, which
> +                * is enabled when the live-migration starts.
> +                */
> +               if ((dev->features ^ features) & ~(1ULL >> VHOST_F_LOG_ALL)) {

The 1 should be shifted to the left:

  1ULL << VHOST_F_LOG_ALL


> +                       RTE_LOG(ERR, VHOST_CONFIG,
> +                               "(%d) features changed while device is running.\n",
> +                               dev->vid);
> +                       return -1;
> +               }
> +
>                 if (dev->notify_ops->features_changed)
>                         dev->notify_ops->features_changed(dev->vid, features);
>         }
> --
> 2.14.3
>
  

On 12/04/2017 03:17 PM, Ladi Prosek wrote:
> On Mon, Dec 4, 2017 at 3:08 PM, Maxime Coquelin
> <maxime.coquelin@redhat.com>  wrote:
>> As section 2.2 of the Virtio spec states about features
>> negotiation:
>> "During device initialization, the driver reads this and tells
>> the device the subset that it accepts. The only way to
>> renegotiate is to reset the device."
>>
>> This patch implements a check to prevent illegal features change
>> while the device is running.
>>
>> One exception is the VHOST_F_LOG_ALL feature bit, which is enabled
>> when live-migration is initiated. But this feature is not negotiated
>> with the Virtio driver, but directly with the Vhost master.
>>
>> Signed-off-by: Maxime Coquelin<maxime.coquelin@redhat.com>
>> ---
>>   lib/librte_vhost/vhost_user.c | 17 ++++++++++++++++-
>>   1 file changed, 16 insertions(+), 1 deletion(-)
>>
>> diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
>> index f4c7ce462..f51055ab2 100644
>> --- a/lib/librte_vhost/vhost_user.c
>> +++ b/lib/librte_vhost/vhost_user.c
>> @@ -183,7 +183,22 @@ vhost_user_set_features(struct virtio_net *dev, uint64_t features)
>>                  return -1;
>>          }
>>
>> -       if ((dev->flags & VIRTIO_DEV_RUNNING) && dev->features != features) {
>> +       if (dev->features == features)
>> +               return 0;
>> +
>> +       if (dev->flags & VIRTIO_DEV_RUNNING) {
>> +               /*
>> +                * Error out if master tries to change features while device is
>> +                * in running state. The exception being VHOST_F_LOG_ALL, which
>> +                * is enabled when the live-migration starts.
>> +                */
>> +               if ((dev->features ^ features) & ~(1ULL >> VHOST_F_LOG_ALL)) {
> The 1 should be shifted to the left:
> 
>    1ULL << VHOST_F_LOG_ALL

Oh right, of course.

Thanks for spotting this.
Maxime