f/linux: log_check WARNING on c3a-standard-4

[Manuel Diewald]

log_check/kernel_tainted tests will fail on AmpereOne based machines like c3a-standard-4 for focal:linux 5.4.0-168.186 and newer. The kernel will issue the following warning and consequently taint the kernel:

[ 0.022227] WARNING: CPU: 1 PID: 17 at arch/arm64/kernel/cpu_errata.c:1387 spectre_bhb_enable_mitigation+0x130/0x250
[ 0.022229] Modules linked in:
[ 0.022232] CPU: 1 PID: 17 Comm: migration/1 Not tainted 5.4.0-172-generic #190-Ubuntu
[ 0.022234] pstate: 20400085 (nzCv daIf +PAN -UAO)
[ 0.022236] pc : spectre_bhb_enable_mitigation+0x130/0x250
[ 0.022237] lr : spectre_bhb_enable_mitigation+0x104/0x250
[ 0.022238] sp : ffff8000100fbcf0
[ 0.022239] x29: ffff8000100fbcf0 x28: 0000000000000002
[ 0.022241] x27: ffff80001003bd10 x26: 0000000000000000
[ 0.022242] x25: 0000000000000060 x24: 0000000000000000
[ 0.022243] x23: 0000000000000001 x22: ffffd491a3079380
[ 0.022244] x21: ffffd491a2395890 x20: ffffd491a32a4518
[ 0.022246] x19: ffffd491a32a4508 x18: 0000000000000030
[ 0.022247] x17: 000000007474b4b6 x16: 0000000092b3f138
[ 0.022248] x15: ffff4ba4fa21eff0 x14: ffffffffffffffff
[ 0.022249] x13: 0000000000000040 x12: 0000000000000001
[ 0.022250] x11: ffffd491a225efa0 x10: 0000000000000b00
[ 0.022252] x9 : ffff8000100fbd30 x8 : ffff4ba4fa26f620
[ 0.022253] x7 : 0000000000000000 x6 : ffffd491a1e33008
[ 0.022254] x5 : 00000000ff0ffff0 x4 : 0000000000f0000f
[ 0.022255] x3 : 00000000c00fac30 x2 : 000000000000000b
[ 0.022256] x1 : ffffd491a32a4508 x0 : 000000000000000b
[ 0.022258] Call trace:
[ 0.022259] spectre_bhb_enable_mitigation+0x130/0x250
[ 0.022261] cpu_enable_non_boot_scope_capabilities+0x6c/0xa8
[ 0.022264] multi_cpu_stop+0xac/0x188
[ 0.022265] cpu_stopper_thread+0xec/0x190
[ 0.022267] smpboot_thread_fn+0x150/0x1d0
[ 0.022269] kthread+0xf0/0x118
[ 0.022271] ret_from_fork+0x10/0x18

The warning was introduced with upstream commit

f41cab7a4653 arm64: Add AMPERE1 to the Spectre-BHB affected list

that came with upstream stable release v5.4.253 as part of Ubuntu-5.4.0-168.186: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2038652

Looking at the code, this warning will always be issued on AMPERE1 based machines but Spectre-BHB mitigation should be guaranteed regardless.