Re: [Xen-devel] Please apply "partially revert "xen: Remove event channel..."

["Raslan, KarimAllah" <karahmed@xxxxxxxxx>]

> On Apr 11, 2017, at 10:57 AM, Juergen Gross <jgross@xxxxxxxx> wrote:
> 
> On 10/04/17 17:32, Raslan, KarimAllah wrote:
>> 
>> Ahmed, Karim Allah
>> karahmed@xxxxxxxxx
>> 
>> 
>> 
>>> On Apr 10, 2017, at 3:57 PM, Juergen Gross <jgross@xxxxxxxx> wrote:
>>> 
>>> On 10/04/17 15:47, Boris Ostrovsky wrote:
>>>> On 04/07/2017 06:11 PM, Stefano Stabellini wrote:
>>>>> On Fri, 7 Apr 2017, Boris Ostrovsky wrote:
>>>>>> On 04/07/2017 01:36 PM, Stefano Stabellini wrote:
>>>>>>> On Fri, 7 Apr 2017, Boris Ostrovsky wrote:
>>>>>>>> On 04/07/2017 07:58 AM, Ian Jackson wrote:
>>>>>>>>> tl;dr:
>>>>>>>>> Please apply
>>>>>>>>> 
>>>>>>>>>   da72ff5bfcb02c6ac8b169a7cf597a3c8e6c4de1
>>>>>>>>>   partially revert "xen: Remove event channel notification through
>>>>>>>>>     Xen PCI platform device"
>>>>>>>>> 
>>>>>>>>> to all stable branches which have a version of the original broken
>>>>>>>>> commit.  This includes at least 4.9.y.
>>>>>>>>> 
>>>>>>>>> Background:
>>>>>>>>> 
>>>>>>>>> osstest service owner writes ("[linux-4.9 baseline test] 107238: 
>>>>>>>>> tolerable FAIL"):
>>>>>>>>> ...
>>>>>>>>>> test-amd64-amd64-qemuu-nested-intel 13 xen-boot/l1  fail never pass
>>>>>>>>> osstest doesn't consider this a regresion because it looks for
>>>>>>>>> regressions within a branch, and this is the first test of Linux 4.9.
>>>>>>>>> However, this is a regression from the kernel we are currently using.
>>>>>>>>> 
>>>>>>>>> L1 dom0 console log:
>>>>>>>>> http://logs.test-lab.xenproject.org/osstest/logs/107238/test-amd64-amd64-qemuu-nested-intel/huxelrebe0---var-log-xen-osstest-serial-l1.guest.osstest.log
>>>>>>>>> 
>>>>>>>>> It seems to have got stuck halfway through booting.
>>>>>>>>> 
>>>>>>>>> The message
>>>>>>>>> (XEN) *** Serial input -> Xen (type 'CTRL-x' three times to switch 
>>>>>>>>> input to DOM0)
>>>>>>>>> shows where osstest timed out on this test, and started its log
>>>>>>>>> capture process (including collecting debug key output).
>>>>>>>>> 
>>>>>>>>> Complete logs for this job here:
>>>>>>>>> http://logs.test-lab.xenproject.org/osstest/logs/107238/test-amd64-amd64-qemuu-nested-intel/info.html
>>>>>>>>> 
>>>>>>>>> Juergen Gross tells me that this is due to the lack of
>>>>>>>>> da72ff5bfcb02c6ac8b169a7cf597a3c8e6c4de1.
>>>>>>>>> 
>>>>>>>>> Thanks,
>>>>>>>>> Ian.
>>>>>>>>> 
>>>>>>>>> PS: Stefano, Boris: did you already request a backport of this commit?
>>>>>>>>> If not, why not ?
>>>>>>>> No, but this should indeed be backported to 4.9+
>>>>>>> Boris, are you going to do that?
>>>>>> Is there anything that needs to be done beyond just applying it to 4.9
>>>>>> (4.10 apparently already has it).
>>>>> No, I don't think so. 4.9 already has the offending commit.
>>>> 
>>>> 
>>>> Looks like there will be a new version of the original patch
>>>> (72a9b186292) so we should hold off with backport request to 4.9:
>>>> 
>>>> https://lists.xenproject.org/archives/html/xen-devel/2017-04/msg01468.html
>>> 
>>> TBH: I'm not convinced by the reasoning why 72a9b186292 has to be
>>> reworked: Do we really care for Xen versions < 4.0 and a theoretical
>>> problem (after all the author admitted the bug isn't being hit in
>>> reality due to a short-circuit in the code)?
>> 
>> IMHO, even if 72a9b186292 has not been reworked we should completely revert 
>> it
>> not only partially revert it. Before this commit at least kernel 4.9+ would
>> work on older Xen versions (< 4.0) while now, it will not even boot.
> 
> Just to make sure we understand which Xen versions are to be
> supported: which Xen versions are you at Amazon currently using?

The majority of Amazon fleet is > 4.0 (4.2) but some old generation stuff
is still running Xen 3.4.

> 
> 
> Juergen

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