riscv: mm: init: try best to use IS_ENABLED(CONFIG_64BIT) instead of #ifdef

Try our best to replace the conditional compilation using
"#ifdef CONFIG_64BIT" by a check for "IS_ENABLED(CONFIG_64BIT)", to
simplify the code and to increase compile coverage.

Now we can also remove the __maybe_unused used in max_mapped_addr
declaration.

We also remove the BUG_ON check of mapping the last 4K bytes of the
addressable memory since this is always true for every kernel actually.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Reviewed-by: Alexandre Ghiti <alex@ghiti.fr>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Author: xhackerustc

arch/riscv/mm/init.c

@@ -102,10 +102,9 @@ static void __init print_vm_layout(void)
 		  (unsigned long)VMALLOC_END);
 	print_mlm("lowmem", (unsigned long)PAGE_OFFSET,
 		  (unsigned long)high_memory);
-#ifdef CONFIG_64BIT
-	print_mlm("kernel", (unsigned long)KERNEL_LINK_ADDR,
-		  (unsigned long)ADDRESS_SPACE_END);
-#endif
+	if (IS_ENABLED(CONFIG_64BIT))
+		print_mlm("kernel", (unsigned long)KERNEL_LINK_ADDR,
+			  (unsigned long)ADDRESS_SPACE_END);
 }
 #else
 static void print_vm_layout(void) { }
@@ -163,7 +162,7 @@ static void __init setup_bootmem(void)
 {
 	phys_addr_t vmlinux_end = __pa_symbol(&_end);
 	phys_addr_t vmlinux_start = __pa_symbol(&_start);
-	phys_addr_t __maybe_unused max_mapped_addr;
+	phys_addr_t max_mapped_addr;
 	phys_addr_t phys_ram_end;
 
 #ifdef CONFIG_XIP_KERNEL
@@ -172,25 +171,23 @@ static void __init setup_bootmem(void)
 
 	memblock_enforce_memory_limit(memory_limit);
 
-	/*
-	 * Reserve from the start of the kernel to the end of the kernel
-	 */
-#if defined(CONFIG_64BIT) && defined(CONFIG_STRICT_KERNEL_RWX)
 	/*
 	 * Make sure we align the reservation on PMD_SIZE since we will
 	 * map the kernel in the linear mapping as read-only: we do not want
 	 * any allocation to happen between _end and the next pmd aligned page.
 	 */
-	vmlinux_end = (vmlinux_end + PMD_SIZE - 1) & PMD_MASK;
-#endif
+	if (IS_ENABLED(CONFIG_64BIT) && IS_ENABLED(CONFIG_STRICT_KERNEL_RWX))
+		vmlinux_end = (vmlinux_end + PMD_SIZE - 1) & PMD_MASK;
+	/*
+	 * Reserve from the start of the kernel to the end of the kernel
+	 */
 	memblock_reserve(vmlinux_start, vmlinux_end - vmlinux_start);
 
 
 	phys_ram_end = memblock_end_of_DRAM();
 #ifndef CONFIG_XIP_KERNEL
 	phys_ram_base = memblock_start_of_DRAM();
 #endif
-#ifndef CONFIG_64BIT
 	/*
 	 * memblock allocator is not aware of the fact that last 4K bytes of
 	 * the addressable memory can not be mapped because of IS_ERR_VALUE
@@ -200,10 +197,11 @@ static void __init setup_bootmem(void)
 	 * address space is occupied by the kernel mapping then this check must
 	 * be done as soon as the kernel mapping base address is determined.
 	 */
-	max_mapped_addr = __pa(~(ulong)0);
-	if (max_mapped_addr == (phys_ram_end - 1))
-		memblock_set_current_limit(max_mapped_addr - 4096);
-#endif
+	if (!IS_ENABLED(CONFIG_64BIT)) {
+		max_mapped_addr = __pa(~(ulong)0);
+		if (max_mapped_addr == (phys_ram_end - 1))
+			memblock_set_current_limit(max_mapped_addr - 4096);
+	}
 
 	min_low_pfn = PFN_UP(phys_ram_base);
 	max_low_pfn = max_pfn = PFN_DOWN(phys_ram_end);
@@ -617,14 +615,6 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 	BUG_ON((PAGE_OFFSET % PGDIR_SIZE) != 0);
 	BUG_ON((kernel_map.phys_addr % PMD_SIZE) != 0);
 
-#ifdef CONFIG_64BIT
-	/*
-	 * The last 4K bytes of the addressable memory can not be mapped because
-	 * of IS_ERR_VALUE macro.
-	 */
-	BUG_ON((kernel_map.virt_addr + kernel_map.size) > ADDRESS_SPACE_END - SZ_4K);
-#endif
-
 	pt_ops.alloc_pte = alloc_pte_early;
 	pt_ops.get_pte_virt = get_pte_virt_early;
 #ifndef __PAGETABLE_PMD_FOLDED
@@ -736,10 +726,9 @@ static void __init setup_vm_final(void)
 		}
 	}
 
-#ifdef CONFIG_64BIT
 	/* Map the kernel */
-	create_kernel_page_table(swapper_pg_dir, false);
-#endif
+	if (IS_ENABLED(CONFIG_64BIT))
+		create_kernel_page_table(swapper_pg_dir, false);
 
 	/* Clear fixmap PTE and PMD mappings */
 	clear_fixmap(FIX_PTE);