Re: Early backport of Vhost regression fix in LTS branches

[Kevin Traynor <ktraynor@redhat.com>]

On 20/09/2022 12:10, Luca Boccassi wrote:
> On Tue, 20 Sept 2022 at 12:03, Kevin Traynor <ktraynor@redhat.com> wrote:
>>
>> On 20/09/2022 10:36, Maxime Coquelin wrote:
>>> Hi LTS maintainers,
>>>
>>> We have discovered a regression causing deadlock in application using
>>> the Vhost library (when vIOMMU is used & NUMA reallocation happens).
>>>
>>> The faulty commit [0] got backported in all maintained LTS branches,
>>> following minor releases are impacted:
>>> - V21.11.1+
>>> - V20.11.5+
>>> - V19.11.12+
>>>
>>> The fix for this regression is already in main branch, and will be part
>>> of next v22.11 release.
>>>
>>> Discussing with Kevin, he suggested the fix to be backported early to
>>> all the LTS branches.
>>>
>>
>> This issue is a deadlock likely to occur with an application such as
>> OVS, that uses vIOMMU vhost ports and a multi-NUMA system.
>>
>> In normal circumstances, for example with OVS, we could just recommend
>> users not to upgrade to the latest DPDK LTS releases until the issue is
>> fixed. Where this one gets tricky is that the latest LTS releases
>> contains CVE fixes.
>>
>> At the moment if a user wants the CVE fixes *and* the below deadlock
>> fix, they will have to pick patches themselves. It might help some if
>> the DPDK stable branches (which are still at last release point)
>> backport the fix below early so a user can just pull the branch.
>>
>>> Below is the fix to be backported:
>>>
>>> ======================================================================
>>> commit 0b2a2ca35037d6a5168f0832c11d9858b8ae946a
>>> Author: David Marchand <david.marchand@redhat.com>
>>> Date:   Mon Jul 25 22:32:03 2022 +0200
>>>
>>>        vhost: fix virtqueue use after free on NUMA reallocation
>>>
>>>        translate_ring_addresses (via numa_realloc) may change a virtio
>>> device and
>>>        virtio queue.
>>>        The virtqueue object must be refreshed before accessing the lock.
>>>
>>>        Fixes: 04c27cb673b9 ("vhost: fix unsafe vring addresses modifications")
>>>        Cc: stable@dpdk.org
>>>
>>>        Signed-off-by: David Marchand <david.marchand@redhat.com>
>>>        Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
>>> ======================================================================
>>>
>>> The fix can be backported without conflicts to all the LTS branches,
>>> except for v19.11, for which the Vhost directory rename can cause
>>> issues. It can be overcome using below command:
>>>
>>> git cherry-pick -Xfind-renames=5% 0b2a2ca350
>>>
>>> Is that OK for you?
>>>
>>
>> I can take care of it for all branches if other maintainers are busy and
>> ok with that.
> 
> Sounds good to me, feel free to go ahead for 20.11, thank you.
> 

20.11 and 21.11 are done.

@Christian, wasn't able to get in touch, not sure if you are on PTO etc.
I don't see any big risk, this is just backporting a patch that would be 
backported in a couple of months anyway. So let's say I will push to the 
19.11 branch on Monday if there are no objections.

thanks,
Kevin.

> Kind regards,
> Luca Boccassi
>