On Fri, 26 Nov 2021 12:11:53 +0800, Xiaoming Ni wrote:

When CONFIG_FSL_PMC is set to n, no value is assigned to cpu_up_prepare
 in the mpc85xx_pm_ops structure. As a result, oops is triggered in
 smp_85xx_start_cpu().

	[    0.627233] smp: Bringing up secondary CPUs ...
	[    0.681659] kernel tried to execute user page (0) - exploit attempt? (uid: 0)
	[    0.766618] BUG: Unable to handle kernel instruction fetch (NULL pointer?)
	[    0.848899] Faulting instruction address: 0x00000000
	[    0.908273] Oops: Kernel access of bad area, sig: 11 [#1]
	...
	[    1.758220] NIP [00000000] 0x0
	[    1.794688] LR [c0021d2c] smp_85xx_kick_cpu+0xe8/0x568
	[    1.856126] Call Trace:
	[    1.885295] [c1051da8] [c0021cb8] smp_85xx_kick_cpu+0x74/0x568 (unreliable)
	[    1.968633] [c1051de8] [c0011460] __cpu_up+0xc0/0x228
	[    2.029038] [c1051e18] [c0031bbc] bringup_cpu+0x30/0x224
	[    2.092572] [c1051e48] [c0031f3c] cpu_up.constprop.0+0x180/0x33c
	[    2.164443] [c1051e88] [c00322e8] bringup_nonboot_cpus+0x88/0xc8
	[    2.236326] [c1051eb8] [c07e67bc] smp_init+0x30/0x78
	[    2.295698] [c1051ed8] [c07d9e28] kernel_init_freeable+0x118/0x2a8
	[    2.369641] [c1051f18] [c00032d8] kernel_init+0x14/0x124
	[    2.433176] [c1051f38] [c0010278] ret_from_kernel_thread+0x14/0x1c

[...]

Applied to powerpc/fixes.

[1/1] powerpc/85xx: fix oops when CONFIG_FSL_PMC=n
      https://git.kernel.org/powerpc/c/3dc709e518b47386e6af937eaec37bb36539edfd

cheers