[0/7] Implement MPIPL for PowerNV

Message

Aditya Gupta Feb. 17, 2025, 7:19 a.m. UTC

Overview
=========

Implemented MPIPL (Memory Preserving IPL, aka fadump) on PowerNV machine
in QEMU.

Note: It's okay if this isn't merged as there might be less users. Sending
for archieval purpose, as the patches can be referred for how fadump/mpipl
can be implemented in baremetal/PowerNV/any other arch QEMU.

Fadump is an alternative dump mechanism to kdump, in which we the firmware
does a memory preserving boot, and the second/crashkernel is booted fresh
like a normal system reset, instead of the crashed kernel loading the
second/crashkernel in case of kdump.

MPIPL in PowerNV, is similar to fadump in Pseries. The idea is same, memory
preserving, where in PowerNV we are assisted by SBE (Self Boot Engine) &
Hostboot, while in Pseries we are assisted by PHyp (Power Hypervisor)

For implementing in baremetal/powernv QEMU, we need to export a
"ibm,opal/dump" node in the device tree, to tell the kernel we support
MPIPL

Once kernel sees the support, and "fadump=on" is passed on commandline,
kernel will register memory regions to preserve with Skiboot.

Kernel sends these data using OPAL calls, after which skiboot/opal saves
the memory region details to MDST and MDDT tables (S-source, D-destination)

Skiboot then triggers the "S0 Interrupt" to the SBE (Self Boot Engine),
along with OPAL's relocated base address.

SBE then stops all core clocks, and only does particular ISteps for a
memory preserving boot.

Then, hostboot comes up, and with help of the relocated base address, it
accesses MDST & MDDT tables (S-source and D-destination), and preserves the
memory regions according to the data in these tables.
And after preserving, it writes the preserved memory region details to MDRT
tables (R-Result), for the kernel to know where/whether a memory region is
preserved.

Both SBE's and hostboot responsiblities have in implemented in the SBE code
in QEMU.

Then in the second kernel/crashkernel boot, OPAL passes the "mpipl-boot"
property for the kernel to know that a dump is active, which kernel then
exports in /proc/vmcore

Git Tree for Testing
====================

https://github.com/adi-g15-ibm/qemu/tree/fadump-powernv-v1

Known Issues
============

* CPU save area has not been implemented

Aditya Gupta (7):
  hw/ppc: Log S0/S1 Interrupt triggers by OPAL
  hw/ppc: Implement S0 SBE interrupt as cpu_pause then host reset
  hw/ppc: Handle stash command in PowerNV SBE
  hw/ppc: Add MDST/MDDT/MDRT table structures and offsets
  hw/ppc: Preserve Memory Regions as per MDST/MDDT tables
  hw/ppc: [WIP] Add Processor Dump Area offsets in Pnv SBE
  hw/ppc: Implement MPIPL in PowerNV

 hw/ppc/pnv.c             |  49 +++++++
 hw/ppc/pnv_sbe.c         | 295 +++++++++++++++++++++++++++++++++++++--
 include/hw/ppc/pnv_sbe.h |   7 +
 3 files changed, 342 insertions(+), 9 deletions(-)

Comments

Nicholas Piggin Feb. 27, 2025, 3:37 a.m. UTC | #1

On Mon Feb 17, 2025 at 5:19 PM AEST, Aditya Gupta wrote:
> Overview
> =========
>
> Implemented MPIPL (Memory Preserving IPL, aka fadump) on PowerNV machine
> in QEMU.

Wow, that's a lot of effort.

> Note: It's okay if this isn't merged as there might be less users. Sending
> for archieval purpose, as the patches can be referred for how fadump/mpipl
> can be implemented in baremetal/PowerNV/any other arch QEMU.

I would like to add it. It helps test a bunch of code that is in Linux
and skiboot, so it would be quite useful. A functional test would be
important to have.

I've had a glance through it, but better review might have to wait for
until the next development cycle.

Thanks,
Nick

Aditya Gupta Feb. 27, 2025, 6:23 a.m. UTC | #2

Hi Nick,

On 27/02/25 09:07, Nicholas Piggin wrote:
> On Mon Feb 17, 2025 at 5:19 PM AEST, Aditya Gupta wrote:
>> Overview
>> =========
>>
>> Implemented MPIPL (Memory Preserving IPL, aka fadump) on PowerNV machine
>> in QEMU.
> Wow, that's a lot of effort.

Thanks Nick.


>> Note: It's okay if this isn't merged as there might be less users. Sending
>> for archieval purpose, as the patches can be referred for how fadump/mpipl
>> can be implemented in baremetal/PowerNV/any other arch QEMU.
> I would like to add it. It helps test a bunch of code that is in Linux
> and skiboot, so it would be quite useful. A functional test would be
> important to have.

Sure, it's not complete yet (didn't implement the CPU saving part) as I 
just wanted to do a experiment I did, will improve those things by v2 
then. It might take some time though.

Will look into the functional test thing also.

> I've had a glance through it, but better review might have to wait for
> until the next development cycle.

Sure, that's totally okay. Thank you for looking at it.


Thanks,

- Aditya G

> Thanks,
> Nick