On Sat, 31 Jul 2021, Christophe Leroy wrote:

quoted

We found that reducing memory with the kernel parameter 'mem=464M' 
would prevent the crash.

Below are Stan's notes from the 'git bisect' run. They include an 
additional failure mode that might be of interest. We've also observed 
"Kernel attempted to write user page (c6207c) - exploit attempt?" and 
"kernel BUG at arch/powerpc/kernel/interrupt.c:49!".

Interesting.  Can you provide detailed log of thoose two BUGs ?

I've attached the dmesg output which Stan sent me a few days ago. It 
contains results for 3 different builds run on two different machines 
(Wallstreet-1 and Wallstreet-2).

$ grep Linux.version WS-1-dmesg
[    0.000000] Linux version 5.12.0-pmac (johnson@ThinkPad) (powerpc-linux-gnu-gcc (Debian 8.3.0-2) 8.3.0, GNU ld (GNU Binutils for Debian) 2.31.1) #6 SMP Sat Jul 24 11:49:36 MDT 2021
[    0.000000] Linux version 5.13.0-pmac (johnson@ThinkPad) (powerpc-linux-gnu-gcc (Debian 8.3.0-2) 8.3.0, GNU ld (GNU Binutils for Debian) 2.31.1) #5 SMP Sat Jul 24 11:00:06 MDT 2021
[    0.000000] Linux version 5.14.0-rc2-pmac-00323-gd8079fac1681 (johnson@ThinkPad) (powerpc-linux-gnu-gcc (Debian 8.3.0-2) 8.3.0, GNU ld (GNU Binutils for Debian) 2.31.1) #7 SMP Sun Jul 25 09:14:32 MDT 2021

$ grep Linux.version WS-2-dmesg
[    0.000000] Linux version 5.12.0-pmac (johnson@ThinkPad) (powerpc-linux-gnu-gcc (Debian 8.3.0-2) 8.3.0, GNU ld (GNU Binutils for Debian) 2.31.1) #6 SMP Sat Jul 24 11:49:36 MDT 2021
[    0.000000] Linux version 5.13.0-pmac (johnson@ThinkPad) (powerpc-linux-gnu-gcc (Debian 8.3.0-2) 8.3.0, GNU ld (GNU Binutils for Debian) 2.31.1) #5 SMP Sat Jul 24 11:00:06 MDT 2021
[    0.000000] Linux version 5.14.0-rc2-pmac-00323-gd8079fac1681 (johnson@ThinkPad) (powerpc-linux-gnu-gcc (Debian 8.3.0-2) 8.3.0, GNU ld (GNU Binutils for Debian) 2.31.1) #7 SMP Sun Jul 25 09:14:32 MDT 2021