Re: [PATCH v6 0/3] XSA-343 followup patches

[Jan Beulich <jbeulich@xxxxxxxx>]

On 18.11.2020 09:41, Jürgen Groß wrote:
> On 18.11.20 09:22, Jan Beulich wrote:
>> On 17.11.2020 19:13, Julien Grall wrote:
>>> On 09/11/2020 16:38, Juergen Gross wrote:
>>>> Juergen Gross (3):
>>>>     xen/events: access last_priority and last_vcpu_id together
>>>>     xen/evtchn: rework per event channel lock
>>>>     xen/evtchn: revert 52e1fc47abc3a0123
>>>
>>> While looking at the list of commits, I noticed that the first patch
>>> hasn't been committed. They were all acked/reviewed, so I am a bit
>>> puzzled why this was omitted...
>>>
>>> I have nearly missed as I was expecting the 3 patches to be committed
>>> together. May I suggest that in the future we reply to the cover letter
>>> and mention which patches are (or not) committed?
>>>
>>> Regarding patch #1, I will commit it tomorrow unless there are strong
>>> objections against.
>>
>> Without a clear outline of what would break with the present logic,
>> I had previously indicated I'm not convinced of the change. This
>> isn't a strong objection, no, but I still wouldn't want to see my
>> name associated with it in such a case. Furthermore I clearly view
>> this as not a backporting candidate, while the other two are (as I
>> did previously indicate). Hence the latter two patches wanted
>> re-basing ahead of the first one anyway, to ease the backports.
> 
> Consider an NMI during evtchn_fifo_set_pending() between updating
> last_vcpu_id and last_priority, while on another cpu a concurrent
> evtchn_fifo_set_pending() is being called. On that other cpu
> lock_old_queue() might return a wrong queue as it will read only
> the new last_vcpu_id, but not the new last_priority value.

Which has become possible only as of patch 2 of this series, i.e.
this one really was a prereq without its description making this
clear. Now that it'll go in on top of the other two, there's no
strict need to change the description anymore, though. But I take
from this that I should also queue it up for backporting then.

Jan