Re: [Qemu-devel] [PATCH v2] ppc: spapr-rtas - implement os-term rtas call

[Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>]

Nikunj A Dadhania <nikunj@linux.vnet.ibm.com> writes:

> Alexander Graf <agraf@suse.de> writes:
>
>> On 17.06.14 11:59, Nikunj A Dadhania wrote:
>>> Alexander Graf <agraf@suse.de> writes:
>>>> On 17.06.14 11:30, Nikunj A Dadhania wrote:
>>>>> Alexander Graf <agraf@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 <anton@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 <anton@samba.org>
>     Signed-off-by: Benjamin Herrenschmidt <benh@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.

Regards,
Nikunj