riscv: Remove redundant restriction on memory size

The original reason for reserving the top 4GiB of the direct map
(space for modules/BPF/kernel) hasn't applied since the address
map was reworked for KASAN.

Signed-off-by: Stuart Menefy <stuart.menefy@codasip.com>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20240624121723.2186279-1-stuart.menefy@codasip.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Author: Stuart Menefy

arch/riscv/mm/init.c

@@ -1132,13 +1132,7 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 	kernel_map.va_pa_offset = IS_ENABLED(CONFIG_64BIT) ?
 				0UL : PAGE_OFFSET - kernel_map.phys_addr;
 
-	/*
-	 * The default maximal physical memory size is KERN_VIRT_SIZE for 32-bit
-	 * kernel, whereas for 64-bit kernel, the end of the virtual address
-	 * space is occupied by the modules/BPF/kernel mappings which reduces
-	 * the available size of the linear mapping.
-	 */
-	memory_limit = KERN_VIRT_SIZE - (IS_ENABLED(CONFIG_64BIT) ? SZ_4G : 0);
+	memory_limit = KERN_VIRT_SIZE;
 
 	/* Sanity check alignment and size */
 	BUG_ON((PAGE_OFFSET % PGDIR_SIZE) != 0);