[dpdk-stable] [PATCH] vhost: prevent disabled rings to be processed with zero-copy

[Maxime Coquelin]

On 2/27/19 11:10 AM, Tiwei Bie wrote:
> On Wed, Feb 27, 2019 at 09:54:28AM +0100, Maxime Coquelin wrote:
>> The vhost-user spec says that once the vring is disabled, the
>> client has to stop processing it. But it can happen when
>> dequeue zero-copy is enabled if outstanding descriptors buffers
>> are still being processed by an extranl NIC or another guest.
> 
> s/extranl/external/
> 
>>
>> The fix consists in draining the zmbufs list to ensure no more
>> descriptors buffers are in the wild.
>>
>> Note that this fix is only working in the case REPLY_ACK
>> protocol feature is enabled, which is not the case by default
>> for now (it is only enabled when IOMMU feature is enabled in
>> the vhost library).
>>
>> Fixes: b0a985d1f340 ("vhost: add dequeue zero copy")
>> Cc: stable at dpdk.org
>>
>> Signed-off-by: Maxime Coquelin <maxime.coquelin at redhat.com>
>> ---
>>   lib/librte_vhost/vhost_user.c | 4 ++++
>>   1 file changed, 4 insertions(+)
>>
>> diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
>> index 36c0c676d..ef947b90c 100644
>> --- a/lib/librte_vhost/vhost_user.c
>> +++ b/lib/librte_vhost/vhost_user.c
>> @@ -1336,6 +1336,10 @@ vhost_user_set_vring_enable(struct virtio_net **pdev,
>>   		"set queue enable: %d to qp idx: %d\n",
>>   		enable, index);
>>   
>> +	/* On disable, rings have to be stopped being processed. */
>> +	if (!enable && dev->dequeue_zero_copy)
>> +		drain_zmbuf_list(dev->virtqueue[index]);
> 
> It might be better to drain the zmbufs list after calling
> application's vring_state_changed() callback, so there will
> be a chance for applications to take some actions first if
> they want.

Good point, I'll fix it in v2.

> Overall this looks good to me,
> 
> Reviewed-by: Tiwei Bie <tiwei.bie at intel.com>
> 
> Thanks!
> Tiwei
>