[PATCH 0/2] powerpc/xive: fix CPU hot unplug

[Cédric Le Goater]

Hello Michael,

On 10/03/2017 01:23 PM, Michael Ellerman wrote:
> Cédric Le Goater <clg at kaod.org> writes:
> 
>> On 09/23/2017 10:26 AM, Cédric Le Goater wrote:
>>> Hi,
>>>
>>> Here are a couple of small fixes to support CPU hot unplug. There are
>>> still some issues to be investigated as, in some occasions, after a
>>> couple of plug and unplug, the cpu which was removed receives a 'lost'
>>> interrupt. This showed to be the decrementer under QEMU.
>>
>> So this seems to be a QEMU issue only which can be solved by 
>> removing the DEE bit from the LPCR on P9 processor when the CPU 
>> is stopped in rtas. PECE3 bit on P8 processors. 
>>
>> I think these patches are valuable fixes for 4.14. The first 
>> is trivial and the second touches the common xive part but it
>> is only called on the pseries platform.  
>>
>> Could you please take a look ? 
> 
> I can.
> 
> You didn't give me much indication in the change logs of what the
> failure mode is if I _don't_ have the fixes, which makes it hard for me
> to assess the severity.
Support for CPU removal came recently on PowerVM and was not
tested when the patchset was sent. A couple of cleanups of the 
XIVE internal structures are missing resulting in a kernel crash 
when the CPU is released. 

There are still some corner cases when stressing the lpar with 
plug/unplug loops. Investigation in progress.  

> Can you flesh out the ".. or else" case in the change logs?

OK. I will improve patch 2 changelog.

> And should both be tagged?
> 
>   Fixes: eac1e731b59e ("powerpc/xive: guest exploitation of the XIVE interrupt controller")
yes I think so. These patches are too small to be tagged as 
adding hotplug support.

Thanks,

C.