Alexander Graf <ag...@suse.de> writes:
> On 25.06.14 06:36, Nikunj A Dadhania wrote:
>> Nikunj A Dadhania <nik...@linux.vnet.ibm.com> writes:
>>
>>> Alexander Graf <ag...@suse.de> writes:
>>>
>>>> On 17.06.14 11:59, Nikunj A Dadhania wrote:
>>>>> Alexander Graf <ag...@suse.de> writes:
>>>>>> On 17.06.14 11:30, Nikunj A Dadhania wrote:
>>>>>>> Alexander Graf <ag...@suse.de> writes:
>>>>>>>>> + spapr_rtas_register("ibm,os-term", rtas_ibm_os_term);
>>>>>>>>> + spapr_rtas_register("ibm,extended-os-term",
>>>>>>>>> rtas_ibm_ext_os_term);
>>>>>>>> Why do we need the extended-os-term if we don't do anything with it?
>>>>>>> Linux kernel checks for both of them because of legacy:
>>>>>>>
>>>>>>> arch/powerpc/kernel/rtas.c:
>>>>>>>
>>>>>>> void rtas_os_term(char *str)
>>>>>>> {
>>>>>>> [...]
>>>>>>> /*
>>>>>>> * Firmware with the ibm,extended-os-term property is
>>>>>>> guaranteed
>>>>>>> * to always return from an ibm,os-term call. Earlier
>>>>>>> versions without
>>>>>>> * this property may terminate the partition which we want
>>>>>>> to avoid
>>>>>>> * since it interferes with panic_timeout.
>>>>>> But we do not return from the RTAS call, so we don't adhere to the
>>>>>> extended semantics?
>>>>> But you would return without calling os-term call if
>>>>> ibm,extended-os-term isnt registered. For that reason I h ave
>>>>> defined a
>>>>> stub.
>>>> I appreciate the hacker mentality, but Linux explicitly checks on
>>>> ibm,extended-os-term to ensure that the hypervisor does not stop the VM
>>>> when it calls ibm,os-term. However, the implementation above does stop
>>>> the VM when the guest calls ibm,os-term.
>>> Seems to be added to do just that:
>>>
>>> commit e9bbc8cde0e3c33b42ddbe1b02108cb5c97275eb
>>> Author: Anton Blanchard <an...@samba.org>
>>> Date: Thu Feb 18 12:11:51 2010 +0000
>>>
>>> powerpc/pseries: Call ibm,os-term if the ibm,extended-os-term is
>>> present
>>>
>>> We have had issues in the past with ibm,os-term initiating shutdown of
>>> a
>>> partition. This is confusing to the user, especially if panic_timeout
>>> is
>>> non zero.
>>>
>>> The temporary fix was to avoid calling ibm,os-term if a panic_timeout
>>> was set
>>> and since we set it on every boot we basically never call ibm,os-term.
>>>
>>> An extended version of ibm,os-term has since been implemented which
>>> gives us
>>> the behaviour we want:
>>>
>>> "When the platform supports extended ibm,os-term behavior, the
>>> return to the
>>> RTAS will always occur unless there is a kernel assisted dump active
>>> as
>>> initiated by an ibm,configure-kernel-dump call."
>>>
>>> This patch checks for the ibm,extended-os-term property and calls
>>> ibm,os-term
>>> if it exists.
>>>
>>> Signed-off-by: Anton Blanchard <an...@samba.org>
>>> Signed-off-by: Benjamin Herrenschmidt <b...@kernel.crashing.org>
>>
>> I was thinking of the following:
>>
>> 1) Return the RTAS unsupported for extended-os-term
>> 2) A comment in the beginning of the function to suggest that this is a
>> stub need for legacy of PowerVM
>>
>> Please let me know your thoughts.
>
> I think we need to clarify what bug Anton was trying to fix. The
> implementation you're proposing for os-term may "initiate a shutdown
> of a partition", albeit a hard stop usually. Is this what Linux is
> trying to avoid?
Let me put down my understanding:
There are two possible way to handle kernel panic:
1) Kdump service running in guest - already working
2) Pass the kernel panic information to hypervisor - not there in Qemu
pseries
So without kdump service running, if linux kernel hits a panic, its going
to check os-term and extended-os-term, only then its going to call
os-term.
Now for what to do in os-term is the question, at present my code is
putting that to guest paniced state(paused)
> Did PowerVM try to inject a soft shutdown signal into the VM and this
> check is to make sure we don't get that?
In this case, isnt that implementation dependent on what we do in qemu?
> I think we should make 100% sure we understand what situation the fix
> above actually tried to avoid and make sure QEMU doesn't do it.
Regards
Nikunj
