[dpdk-dev] [PATCH v2 2/3] vhost: protect dirty logging against logging base change

[Maxime Coquelin]

Hi Jianfeng,

On 02/14/2018 03:03 AM, Tan, Jianfeng wrote:
> Hi Maxime,
> 
> 
> On 11/28/2017 6:06 PM, Maxime Coquelin wrote:
>>
>>
>> On 11/24/2017 07:08 PM, Maxime Coquelin wrote:
>>> When performing live-migration with multiple queue pairs,
>>> VHOST_USER_SET_LOG_BASE request is sent multiple times.
>>>
>>> If packets are being processed by the PMD threads, it is
>>> possible that they are setting bits in the dirty log map while
>>> its region is being unmapped by the vhost-user protocol thread.
>>> It results in the following crash:
>>> Thread 3 "lcore-slave-2" received signal SIGSEGV, Segmentation fault.
>>> [Switching to Thread 0x7f71ca495700 (LWP 32451)]
>>> 0x00000000004bfc8a in vhost_set_bit (addr=0x7f71cbe18432 <error: 
>>> Cannot access memory at address 0x7f71cbe18432>, nr=1) at 
>>> /home/max/projects/src/mainline/dpdk/lib/librte_vhost/vhost.h:267
>>> 267        __sync_fetch_and_or_8(addr, (1U << nr));
>>>
>>> We can see the vhost-user protocol thread just did the unmap of the
>>> dirty log region when it happens.
>>>
>>> This patch prevents this by introducing a RW lock to protect
>>> the log base.
>>>
>>> Fixes: 54f9e32305d4 ("vhost: handle dirty pages logging request")
>>> Cc: stable at dpdk.org
>>>
>>> Signed-off-by: Maxime Coquelin <maxime.coquelin at redhat.com>
>>> ---
>>>   lib/librte_vhost/vhost.c      |  2 ++
>>>   lib/librte_vhost/vhost.h      | 14 +++++++++++---
>>>   lib/librte_vhost/vhost_user.c |  4 ++++
>>>   3 files changed, 17 insertions(+), 3 deletions(-)
>>>
>>
>> By clarifying the vhost-user spec, we may be able to avoid this lock and
>> just ignore the subsequent SET_LOG_BASE requests once
>> VHOST_F_LOG_ALL feature bit is set.
>>
>> So let's just discard this series for now.
> 
> I would assume this issue has been addressed by the per-queue lock patch 
> from Victor, correct?

Correct.

> Besides, we really don't need multiple unmap/map for each vq. Would you 
> think this shall be fixed in QEMU?

Yes, I tihnk you are right it should be fixed in QEMU, so that it is
sent only for the first queue pair.

But I didn't had time to work on it TBH.


Cheers,
Maxime
> Thanks,
> Jianfeng