Re: [PATCH v1 0/2] powerpc/pseries/cmm: two smaller fixes

David Hildenbrand (Red Hat)
2025-11-28T07:36:11Z

On 11/28/25 06:05, Ritesh Harjani (IBM) wrote:
> "David Hildenbrand (Red Hat)" <david@kernel.org> writes:
>
>> On 10/21/25 12:06, David Hildenbrand wrote:
>>> Two smaller fixes identified while doing a bigger rework.
>>>
>>> Compile-tested only as I don't have an easy way to test right now.
>>>
>>> I would prefer for these patches to go through the MM tree as I will
>>> be sending out a bigger version soon that is based on this series --
>>> I split of the fixes from the other stuff.
>>>
>>
>> Ping,
>>
>> I tried to get CMM running again (using the simulation mode I introduced
>> a while back), but so far my attempts to get a reasonable powernv VM
>> booted in QEMU failed :(
>>
>> (e.g., Fedora qcow2 images use xfs, but the open powernv loader is based
>> on a 5.10 kernel without some mystical XFS feature ...)
>>
>

Hi Ritesh,

> Sorry, I missed seeing this earlier.
>
> Do you have the link to simulation mode which you are referring above
> please? So far I didn't find the support of this beyond Linux LPAR
> (pseries), but maybe I missed it.

When I did a rework of the CMM balloon in 2019, I needed a way to test
it. So I added

commit b1713975c31ae20ecc40fd00191ee3fa51445d4a
Author: David Hildenbrand <david@kernel.org>
Date: Thu Oct 31 15:29:31 2019 +0100

powerpc/pseries/cmm: Simulation mode

Let's allow to test the implementation without needing HW support.
When "simulate=1" is specified when loading the module, we bypass all
HW checks and HW calls. The sysfs file "simulate_loan_target_kb" can
be used to simulate HW requests.

The simualtion mode can be activated using:
modprobe cmm debug=1 simulate=1

And the requested loan target can be changed using:
echo X > /sys/devices/system/cmm/cmm0/simulate_loan_target_kb

I allows for bypassing the absence of FW_FEATURE_CMO.

Back in the days I was able to test it with a pseries (or was it powernv?)
machine we had here at RH. So far my attempts failed to test it in a
similar fashion in QEMU.

--
Cheers

David