riscv: add a warning when physical memory address overflows

The part of physical memory that exceeds the size of the linear mapping
will be discarded. When the system starts up normally, a warning message
will be printed to prevent confusion caused by the mismatch between the
system memory and the actual physical memory.

Signed-off-by: Yunhui Cui <cuiyunhui@bytedance.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Tested-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20240814062625.19794-1-cuiyunhui@bytedance.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/mm/init.c

@@ -256,8 +256,12 @@ static void __init setup_bootmem(void)
 	 */
 	if (IS_ENABLED(CONFIG_64BIT) && IS_ENABLED(CONFIG_MMU)) {
 		max_mapped_addr = __pa(PAGE_OFFSET) + KERN_VIRT_SIZE;
-		memblock_cap_memory_range(phys_ram_base,
-					  max_mapped_addr - phys_ram_base);
+		if (memblock_end_of_DRAM() > max_mapped_addr) {
+			memblock_cap_memory_range(phys_ram_base,
+						  max_mapped_addr - phys_ram_base);
+			pr_warn("Physical memory overflows the linear mapping size: region above %pa removed",
+				&max_mapped_addr);
+		}
 	}
 
 	/*