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

From: Alexander Graf
Subject: Re: [Qemu-ppc] [PATCH v2] ppc: spapr-rtas - implement os-term rtas call
Date: Wed, 25 Jun 2014 13:32:05 +0200
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:24.0) Gecko/20100101 Thunderbird/24.6.0

On 25.06.14 13:27, Nikunj A Dadhania wrote:
Alexander Graf <address@hidden> writes:

On 25.06.14 06:36, Nikunj A Dadhania wrote:
Nikunj A Dadhania <address@hidden> writes:

Alexander Graf <address@hidden> writes:

On 17.06.14 11:59, Nikunj A Dadhania wrote:
Alexander Graf <address@hidden> writes:
On 17.06.14 11:30, Nikunj A Dadhania wrote:
Alexander Graf <address@hidden> 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:


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 
             * 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
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 <address@hidden>
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 <address@hidden>
      Signed-off-by: Benjamin Herrenschmidt <address@hidden>
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

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

It's checking both for a reason. Find that reason.


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