m68k: mm: Fix systems with memory at end of 32-bit address space

The calculation of end addresses of memory chunks overflowed to 0 when
a memory chunk is located at the end of 32-bit address space.
This is the case for the HP300 architecture.

Link: https://lore.kernel.org/linux-m68k/CACz-3rhUo5pgNwdWHaPWmz+30Qo9xCg70wNxdf7o5x-6tXq8QQ@mail.gmail.com/
Signed-off-by: Kars de Jong <jongk@linux-m68k.org>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/r/20230223112349.26675-1-jongk@linux-m68k.org
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

arch/m68k/mm/motorola.c

@@ -437,7 +437,7 @@ void __init paging_init(void)
 	}
 
 	min_addr = m68k_memory[0].addr;
-	max_addr = min_addr + m68k_memory[0].size;
+	max_addr = min_addr + m68k_memory[0].size - 1;
 	memblock_add_node(m68k_memory[0].addr, m68k_memory[0].size, 0,
 			  MEMBLOCK_NONE);
 	for (i = 1; i < m68k_num_memory;) {
@@ -452,21 +452,21 @@ void __init paging_init(void)
 		}
 		memblock_add_node(m68k_memory[i].addr, m68k_memory[i].size, i,
 				  MEMBLOCK_NONE);
-		addr = m68k_memory[i].addr + m68k_memory[i].size;
+		addr = m68k_memory[i].addr + m68k_memory[i].size - 1;
 		if (addr > max_addr)
 			max_addr = addr;
 		i++;
 	}
 	m68k_memoffset = min_addr - PAGE_OFFSET;
-	m68k_virt_to_node_shift = fls(max_addr - min_addr - 1) - 6;
+	m68k_virt_to_node_shift = fls(max_addr - min_addr) - 6;
 
 	module_fixup(NULL, __start_fixup, __stop_fixup);
 	flush_icache();
 
-	high_memory = phys_to_virt(max_addr);
+	high_memory = phys_to_virt(max_addr) + 1;
 
 	min_low_pfn = availmem >> PAGE_SHIFT;
-	max_pfn = max_low_pfn = max_addr >> PAGE_SHIFT;
+	max_pfn = max_low_pfn = (max_addr >> PAGE_SHIFT) + 1;
 
 	/* Reserve kernel text/data/bss and the memory allocated in head.S */
 	memblock_reserve(m68k_memory[0].addr, availmem - m68k_memory[0].addr);