linux-kernel - [PATCH 0/2] Disabling NMI watchdog during LPM's memory transfer

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Message-Id: <20220601155315.35109-1-ldufour@linux.ibm.com>
Date:   Wed,  1 Jun 2022 17:53:13 +0200
From:   Laurent Dufour <ldufour@...ux.ibm.com>
To:     mpe@...erman.id.au, benh@...nel.crashing.org, paulus@...ba.org,
        nathanl@...ux.ibm.com, haren@...ux.vnet.ibm.com, npiggin@...il.com
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: [PATCH 0/2] Disabling NMI watchdog during LPM's memory transfer

When a partition is transferred, once it arrives at the destination node,
the partition is active but much of its memory must be transferred from the
start node.

It depends on the activity in the partition, but the more CPU the partition
has, the more memory to be transferred is likely to be. This causes latency
when accessing pages that need to be transferred, and often, for large
partitions, it triggers the NMI watchdog.

The NMI watchdog causes the CPU stack to dump where it appears to be
stuck. In this case, it does not bring much information since it can happen
during any memory access of the kernel.

In addition, the NMI interrupt mechanism is not secure and can generate a
dump system in the event that the interruption is taken while MSR[RI]=0.

Given how often hard lockups are detected when transferring large
partitions, it seems best to disable the watchdog NMI until the memory
transfer from the start node is complete.

The first patch in this series waits for the memory transfer to complete,
the second disables the watchdog NMI just before stopping the CPUs and
reactivates it when the memory transfer is complete.

Laurent Dufour (2):
  powerpc/mobility: Wait for memory transfer to complete
  powerpc/mobility: disabling hard lockup watchdog during LPM

 arch/powerpc/platforms/pseries/mobility.c | 40 +++++++++++++++++++++--
 1 file changed, 38 insertions(+), 2 deletions(-)

-- 
2.36.1