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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 13:03:51 +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 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?

Did PowerVM try to inject a soft shutdown signal into the VM and this check is to make sure we don't get that?

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.


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