Re: [PATCH v2 1/2] vhost: fix memory leak in Virtio Tx split path

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

On 2/6/24 11:29, David Marchand wrote:
> On Wed, Jan 31, 2024 at 8:53 PM Maxime Coquelin
> <maxime.coquelin@redhat.com> wrote:
>>
>> When vIOMMU is enabled and Virtio device is bound to kernel
>> driver in guest, rte_vhost_dequeue_burst() will often return
>> early because of IOTLB misses.
> 
> In theory, we can hit this issue with a dpdk pmd too, as long as the
> vIOMMU is in use.
> But the consequence would be a "really small" leak which does not have
> the same impact as what was seen with the kernel driver which
> maps/unmaps pages associated with virtio-net skb way more often :-).
> So maybe rephrase this part emphasizing on the kernel case like:
> 
> """
> When vIOMMU is enabled, rte_vhost_dequeue_burst() can return early
> because of IOTLB misses.
> Such IOTLB misses are especially frequent when a Virtio device is
> bound to a kernel driver in guest.
> """

Thanks, I agree with your suggestion, Virtio PMD is indeed also
impacted.

>>
>> This patch fixes a mbuf leak occurring in this case.
>>
>> Fixes: 242695f6122a ("vhost: allocate and free packets in bulk in Tx split")
>> Cc: stable@dpdk.org
>>
>> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
>> Signed-off-by: David Marchand <david.marchand@redhat.com>
> 
> Reviewed-by: David Marchand <david.marchand@redhat.com>
> 
>