Re: [dpdk-dev] [PATCH] vhost: fix invalid use of stored last used index

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 5/17/21 12:07 PM, Ling, WeiX wrote:
>> -----Original Message-----
>> From: Maxime Coquelin <maxime.coquelin@redhat.com>
>> Sent: Monday, May 17, 2021 03:38 PM
>> To: Balazs Nemeth <bnemeth@redhat.com>; dev@dpdk.org; Ling, WeiX
>> <weix.ling@intel.com>
>> Subject: Re: [dpdk-dev] [PATCH] vhost: fix invalid use of stored last used
>> index
>>
>> Hi Ling,
>>
>>
>> On 5/14/21 6:02 PM, Balazs Nemeth wrote:
>>> The optimization introduced by commit d18db8049c7c ("vhost: read last
>>> used index once") didn't account for the fact that
>>> vhost_flush_enqueue_shadow_packed increments the last_used_idx. For
>>> this reason, store last_used_idx after the potential call to
>>> vhost_flush_enqueue_shadow_packed.
>>>
>>> Fixes: d18db8049c7c ("vhost: read last used index once")
>>> Signed-off-by: Balazs Nemeth <bnemeth@redhat.com>
>>> ---
>>>  lib/vhost/virtio_net.c | 7 +++++--
>>>  1 file changed, 5 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c index
>>> abfd67d38c..8da8a86a10 100644
>>> --- a/lib/vhost/virtio_net.c
>>> +++ b/lib/vhost/virtio_net.c
>>> @@ -218,14 +218,17 @@ vhost_flush_enqueue_batch_packed(struct
>>> virtio_net *dev,  {
>>>  	uint16_t i;
>>>  	uint16_t flags;
>>> -	uint16_t last_used_idx = vq->last_used_idx;
>>> -	struct vring_packed_desc *desc_base = &vq-
>>> desc_packed[last_used_idx];
>>> +	uint16_t last_used_idx;
>>> +	struct vring_packed_desc *desc_base;
>>>
>>>  	if (vq->shadow_used_idx) {
>>>  		do_data_copy_enqueue(dev, vq);
>>>  		vhost_flush_enqueue_shadow_packed(dev, vq);
>>>  	}
>>>
>>> +	last_used_idx = vq->last_used_idx;
>>> +	desc_base = &vq->desc_packed[last_used_idx];
>>> +
>>>  	flags = PACKED_DESC_ENQUEUE_USED_FLAG(vq-
>>> used_wrap_counter);
>>>
>>>  	vhost_for_each_try_unroll(i, 0, PACKED_BATCH_SIZE) {
>>>
>>
>> Could you please confirm the patch fixes the issue you reported?
>>
>> Thanks,
>> Maxime
> 
> Hi Maxime,
> 
> Apply your patch https://patches.dpdk.org/project/dpdk/patch/83fa6253725a7bc69bccb7897f380422354a2898.1621008025.git.bnemeth@redhat.com/ based on DPDK-21.05-rc3(7989b7e7da9b), tested PASSED.

Thanks for testing with the patch.

Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Tested-by: Wei Ling <weix.ling@intel.com>

Thanks,
Maxime


Thanks,
Maxime


> Regards,
> Ling Wei
>