From: Helge Deller <deller@xxxxxx> commit bf71bc16e02162388808949b179d59d0b571b965 upstream. The Debian kernel v5.6 triggers this kernel panic: Kernel panic - not syncing: Bad Address (null pointer deref?) Bad Address (null pointer deref?): Code=26 (Data memory access rights trap) at addr 0000000000000000 CPU: 0 PID: 0 Comm: swapper Not tainted 5.6.0-2-parisc64 #1 Debian 5.6.14-1 IAOQ[0]: mem_init+0xb0/0x150 IAOQ[1]: mem_init+0xb4/0x150 RP(r2): start_kernel+0x6c8/0x1190 Backtrace: [<0000000040101ab4>] start_kernel+0x6c8/0x1190 [<0000000040108574>] start_parisc+0x158/0x1b8 on a HP-PARISC rp3440 machine with this memory layout: Memory Ranges: 0) Start 0x0000000000000000 End 0x000000003fffffff Size 1024 MB 1) Start 0x0000004040000000 End 0x00000040ffdfffff Size 3070 MB Fix the crash by avoiding virt_to_page() and similar functions in mem_init() until the memory zones have been fully set up. Signed-off-by: Helge Deller <deller@xxxxxx> Cc: stable@xxxxxxxxxxxxxxx # v5.0+ Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/parisc/mm/init.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/arch/parisc/mm/init.c +++ b/arch/parisc/mm/init.c @@ -608,7 +608,7 @@ void __init mem_init(void) > BITS_PER_LONG); high_memory = __va((max_pfn << PAGE_SHIFT)); - set_max_mapnr(page_to_pfn(virt_to_page(high_memory - 1)) + 1); + set_max_mapnr(max_low_pfn); free_all_bootmem(); #ifdef CONFIG_PA11
