KOP L2 guest fails to boot with 1 core - SMT8 topology

[bugproxy]

== Comment: #0 - SEETEENA THOUFEEK <email address hidden> - 2024-06-25 01:24:11 ==
+++ This bug was initially created as a clone of Bug #205277 +++

---Problem Description---
KOP L2 guest fails to boot with 1 core - SMT8 topology

---Additional Hardware Info---
na

---Debugger Data---
na

---Steps to Reproduce---
 KOP L2 guest fails to boot when we set the CPU topology as 1 core - SMT 8

command line used to verify the issue:
#!/bin/sh

QEMU="/home/mgautam/qemu"
qemu-system-ppc64 -s \
-drive file=/root/debian-12-nocloud-ppc64el.qcow2,format=qcow2 \
-m 20G \
-smp 8,cores=1,sockets=1,threads=8 \
-cpu host \
-nographic \
-machine pseries,ic-mode=xics -accel kvm \
-net nic,model=virtio \
-net user,host=10.0.2.10,hostfwd=tcp:127.0.0.1:10022-:22

NOTE: L2 boots fine when doorbells are turned off in L1 kernel

As per the investigation so far, the doorbell exception is not getting fired inside L2 guest. At L1 level, if we set DPDES=1 in the GSB for L2, the guest never receives the doorbell and also it is never cleared from the GSB. We are discussing this behaviour with phyp team.

The root cause of this issue is lack of DPDES support at L1. I've posted the fix upstream - https://<email address hidden>/T/#u

The fix has been accepted upstream and will be backported for kernels >= 6.7

https://<email address hidden>/

---Patches Installed---
na

---System Hang---
 na

---uname output---
na

Contact Information = na

Machine Type = na

Userspace rpm: na

Userspace tool common name: na

The userspace tool has the following bit modes: na

Userspace tool obtained from project website: na

*Additional Instructions for na:
-Post a private note with access information to the machine that is currently in the debugger.
-Attach ltrace and strace of userspace application.

[Frank Heimes (fheimes)]

Hello and thanks for having reported this issue.

Once the patch set 'Fix doorbell emulation for v2 API on PPC' with patches:
- arch/powerpc/kvm: Add DPDES support in helper library for Guest state buffer
- arch/powerpc/kvm: Fix doorbell emulation for v2 API
are upstream accepted (having them in 'linux-next' is sufficient), we can think about picking them.
I cannot find them in 'linux-next' yet (https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/log/?qt=grep&q=Fix+doorbell+emulation+for+v2+API), but assume they are still part of a staging tree and will hit linux-next soon.

Based on your statement "The fix has been accepted upstream and will be backported for kernels >= 6.7" I assume the patch(es) are (or will be soon) also upstream marked as "stable updates", and will then land in kernel 6.8 (that we have in 24.04).
As soon as this happens, the "stable updates" for 6.8 will be picked by the Canonical kernel team automatically.

[bugproxy (bugproxy)]

------- Comment From <email address hidden> 2024-06-25 06:25 EDT-------
Thanks for the response.

The patches are there in linux-next already.

1. https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=55dfb8bed6fe8bda390cc71cca878d11a9407099
2. https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=54ec2bd9e0173b75daf84675d07c56584f96564b

[Frank Heimes (fheimes)]

Looks like the names changed slightly, thanks for pointing the the right upstream commits!

And I see that they are marked as stable updates ("Cc: <email address hidden> # v6.7+"), which is great!
With that they will be soon automatically be picked up by the Canonical kernel team.