Re: [dpdk-dev] [PATCH] vhost: fix segfault as handle set_mem_table message

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

On 12/05/2017 03:19 PM, Yuanhan Liu wrote:
> On Tue, Nov 28, 2017 at 01:09:29PM +0100, Maxime Coquelin wrote:
>>
>>
>> On 11/15/2017 12:41 PM, Jianfeng Tan wrote:
>>> In a running VM, operations (like device attach/detach) will
>>> trigger the QEMU to resend set_mem_table to vhost-user backend.
>>>
>>> DPDK vhost-user handles this message rudely by unmap all existing
>>> regions and map new ones. This might lead to segfault if there
>>> is pmd thread just trying to touch those unmapped memory regions.
>>>
>>> But for most cases, except VM memory hotplug, 

FYI, Victor is working on implementing a lock-less protection mechanism
to prevent crashes in such cases. It is intended first to protect
log_base in case of multiqueue + live-migration, but would solve thi
issue too.

>>>> QEMU still sends the
>>> set_mem_table message even the memory regions are not changed as
>>> QEMU vhost-user filters out those not backed by file (fd > 0).
>>>
>>> To fix this case, we add a check in the handler to see if the
>>> memory regions are really changed; if not, we just keep old memory
>>> regions.
>>>
>>> Fixes: 8f972312b8f4 ("vhost: support vhost-user")
>>>
>>> CC: stable@dpdk.org
>>>
>>> CC: Yuanhan Liu <yliu@fridaylinux.org>
>>> CC: Maxime Coquelin <maxime.coquelin@redhat.com>
>>>
>>> Reported-by: Yang Zhang <zy107165@alibaba-inc.com>
>>> Reported-by: Xin Long <longxin.xl@alibaba-inc.com>
>>> Signed-off-by: Yi Yang <yi.y.yang@intel.com>
>>> Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
>>> ---
>>>   lib/librte_vhost/vhost_user.c | 33 +++++++++++++++++++++++++++++++++
>>>   1 file changed, 33 insertions(+)
>>
>> Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> 
> Applied to dpdk-next-virtio.
> 
> Thanks.
> 
> 	--yliu
> 

Maxime