Re: [Xen-devel] [PATCH] shut down domain when last vCPU goes down

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.02.18 at 16:52, <roger.pau@xxxxxxxxxx> wrote:
> On Fri, Feb 16, 2018 at 08:10:48AM -0700, Jan Beulich wrote:
>> I've just had to deal with an early boot crash of Linux which occurred
>> so early that even "earlyprintk=xen" did not produce any useful output.
>> Hence the domain appeared to hang, while in fact it had brought down its
>> only vCPU. By translating this to a shutdown, the situation will be
>> better recognizable.
>> 
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> 
> I'm wondering, is it common for a domain to shutdown by shutting down
> all it's vCPUs?
> 
> In the scenario that you describe above it seems it would be more
> helpful to issue a SHUTDOWN_crash instead maybe with a gdprintk
> message in order to aid debugging.

Seeing this I was puzzled too; I have no idea why Linux does this,
other than this being an attempt to provide a PV equivalent of the
HLT instruction. But no, SHUTDOWN_crash is not appropriate imo
(and I did consider it) - we can't know what the reason was for the
guest to issue the hypercall; in particular we shouldn't trigger
actions (like dumping) that are likely tied to a crash unless we're
sure there was a crash.

Jan

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