Re: [dpdk-dev] [PATCH] vhost: fix vhost user virtqueue not accessable

[Adrian Moreno <amorenoz@redhat.com>]

On 10/28/19 3:13 AM, Liu, Yong wrote:
> 
> 
>> -----Original Message-----
>> From: Adrian Moreno [mailto:amorenoz@redhat.com]
>> Sent: Friday, October 25, 2019 8:21 PM
>> To: Liu, Yong <yong.liu@intel.com>; maxime.coquelin@redhat.com; Bie, Tiwei
>> <tiwei.bie@intel.com>; Wang, Zhihong <zhihong.wang@intel.com>
>> Cc: dev@dpdk.org
>> Subject: Re: [PATCH] vhost: fix vhost user virtqueue not accessable
>>
>> Hi Marvin,
>>
>> On 10/25/19 6:20 PM, Marvin Liu wrote:
>>> Log feature is disabled in vhost user, so that log address was invalid
>>> when checking. Add feature bit check can skip useless address check.
>>>
>> Just so I understand, what conditions is the log address invalid?
>>
>>> Fixes: 04cfc7fdbfca ("vhost: translate incoming log address to gpa")
>>>
>>> Signed-off-by: Marvin Liu <yong.liu@intel.com>
>>> ---
>>>  lib/librte_vhost/vhost_user.c | 16 +++++++++-------
>>>  1 file changed, 9 insertions(+), 7 deletions(-)
>>>
>>> diff --git a/lib/librte_vhost/vhost_user.c
>> b/lib/librte_vhost/vhost_user.c
>>> index 61ef699ac..0407fdc29 100644
>>> --- a/lib/librte_vhost/vhost_user.c
>>> +++ b/lib/librte_vhost/vhost_user.c
>>> @@ -741,13 +741,15 @@ translate_ring_addresses(struct virtio_net *dev,
>> int vq_index)
>>>  		vq->last_avail_idx = vq->used->idx;
>>>  	}
>>>
>>> -	vq->log_guest_addr =
>>> -		translate_log_addr(dev, vq, addr->log_guest_addr);
>>> -	if (vq->log_guest_addr == 0) {
>>> -		RTE_LOG(DEBUG, VHOST_CONFIG,
>>> -			"(%d) failed to map log_guest_addr .\n",
>>> -			dev->vid);
>>> -		return dev;
>>> +	if (dev->features & (1ULL << VHOST_F_LOG_ALL)) {
>>> +		vq->log_guest_addr =
>>> +			translate_log_addr(dev, vq, addr->log_guest_addr);
>>
>> VHOST_F_LOG_ALL is only negotiated once the migration has started (at least
>> from
>> qemu's perspective).
>> That means that we will postponing the translation  of the log address to
>> the
>> vhost_user_set_vring_addr() call that follows the VHOST_F_LOG_ALL enabling.
>> In
>> that call there are (at least) two things that could go wrong and lead to a
>> migration failure:
>> - If VHOST_USER_F_PROTOCOL_FEATURES is not enabled, the address won't be
>> translated:
>>
>> vhost_user:795
>> 	if ((vq->enabled && (dev->features &
>> 				(1ULL << VHOST_USER_F_PROTOCOL_FEATURES))) ||
>> 			access_ok) {
>> 		dev = translate_ring_addresses(dev, msg->payload.addr.index);
>> 		if (!dev)
>> 			return RTE_VHOST_MSG_RESULT_ERR;
>>
>> 		*pdev = dev;
>> 	}
>>
>> - If the IOMMU is enabled and there's a miss, we would have to wait for the
>> IOTLB_UPDATE and during that time, there would be failed accesses to the
>> (still
>> untranslated) log address.
>>
>>
> 
> Thanks, Adrian. 
> Log address can be zero when logging is not enabled.
> How about add other criteria after translation? Log address will be translated anyway and not affect vq status.
> 
>         vq->log_guest_addr =
>                 translate_log_addr(dev, vq, addr->log_guest_addr);
> -       if (vq->log_guest_addr == 0) {
> +       if (vq->log_guest_addr == 0 && addr->flags) {
>                 RTE_LOG(DEBUG, VHOST_CONFIG,
>                         "(%d) failed to map log_guest_addr .\n",
>                         dev->vid);
>                 return dev;
>         }
> 
That makes perfect sense IMHO. Thank you.

> Meanwhile, log address of packed ring is fixed to zero. Is any special reason to do that? 
> 
No idea to be honest.

Thanks.
Adrian
> Regards,
> Marvin
> 
>>
>>> +		if (vq->log_guest_addr == 0) {
>>> +			RTE_LOG(DEBUG, VHOST_CONFIG,
>>> +				"(%d) failed to map log_guest_addr .\n",
>>> +				dev->vid);
>>> +			return dev;
>>> +		}
>>>  	}
>>>  	vq->access_ok = 1;
>>>
>>>
>> Thanks,
>> Adrian