x86/mm/64: Always use dynamic memory layout

Dynamic memory layout is used by KASLR and 5-level paging.

CONFIG_X86_5LEVEL is going to be removed, making 5-level paging support
unconditional which requires unconditional support of dynamic memory
layout.

Remove CONFIG_DYNAMIC_MEMORY_LAYOUT.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Kieran Bingham <kbingham@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20250516123306.3812286-2-kirill.shutemov@linux.intel.com

Author: kiryl

arch/x86/Kconfig

@@ -1467,7 +1467,6 @@ config X86_PAE
 config X86_5LEVEL
 	bool "Enable 5-level page tables support"
 	default y
-	select DYNAMIC_MEMORY_LAYOUT
 	select SPARSEMEM_VMEMMAP
 	depends on X86_64
 	help
@@ -2168,17 +2167,10 @@ config PHYSICAL_ALIGN
 
 	  Don't change this unless you know what you are doing.
 
-config DYNAMIC_MEMORY_LAYOUT
-	bool
-	help
-	  This option makes base addresses of vmalloc and vmemmap as well as
-	  __PAGE_OFFSET movable during boot.
-
 config RANDOMIZE_MEMORY
 	bool "Randomize the kernel memory sections"
 	depends on X86_64
 	depends on RANDOMIZE_BASE
-	select DYNAMIC_MEMORY_LAYOUT
 	default RANDOMIZE_BASE
 	help
 	  Randomizes the base virtual address of kernel memory sections

arch/x86/include/asm/page_64_types.h

@@ -41,11 +41,7 @@
 #define __PAGE_OFFSET_BASE_L5	_AC(0xff11000000000000, UL)
 #define __PAGE_OFFSET_BASE_L4	_AC(0xffff888000000000, UL)
 
-#ifdef CONFIG_DYNAMIC_MEMORY_LAYOUT
 #define __PAGE_OFFSET           page_offset_base
-#else
-#define __PAGE_OFFSET           __PAGE_OFFSET_BASE_L4
-#endif /* CONFIG_DYNAMIC_MEMORY_LAYOUT */
 
 #define __START_KERNEL_map	_AC(0xffffffff80000000, UL)
 

arch/x86/include/asm/pgtable_64_types.h

@@ -128,15 +128,9 @@ extern unsigned int ptrs_per_p4d;
 #define __VMEMMAP_BASE_L4	0xffffea0000000000UL
 #define __VMEMMAP_BASE_L5	0xffd4000000000000UL
 
-#ifdef CONFIG_DYNAMIC_MEMORY_LAYOUT
 # define VMALLOC_START		vmalloc_base
 # define VMALLOC_SIZE_TB	(pgtable_l5_enabled() ? VMALLOC_SIZE_TB_L5 : VMALLOC_SIZE_TB_L4)
 # define VMEMMAP_START		vmemmap_base
-#else
-# define VMALLOC_START		__VMALLOC_BASE_L4
-# define VMALLOC_SIZE_TB	VMALLOC_SIZE_TB_L4
-# define VMEMMAP_START		__VMEMMAP_BASE_L4
-#endif /* CONFIG_DYNAMIC_MEMORY_LAYOUT */
 
 #ifdef CONFIG_RANDOMIZE_MEMORY
 # define DIRECT_MAP_PHYSMEM_END	direct_map_physmem_end

arch/x86/kernel/head64.c

@@ -59,14 +59,12 @@ unsigned int ptrs_per_p4d __ro_after_init = 1;
 EXPORT_SYMBOL(ptrs_per_p4d);
 #endif
 
-#ifdef CONFIG_DYNAMIC_MEMORY_LAYOUT
 unsigned long page_offset_base __ro_after_init = __PAGE_OFFSET_BASE_L4;
 EXPORT_SYMBOL(page_offset_base);
 unsigned long vmalloc_base __ro_after_init = __VMALLOC_BASE_L4;
 EXPORT_SYMBOL(vmalloc_base);
 unsigned long vmemmap_base __ro_after_init = __VMEMMAP_BASE_L4;
 EXPORT_SYMBOL(vmemmap_base);
-#endif
 
 /* Wipe all early page tables except for the kernel symbol map */
 static void __init reset_early_page_tables(void)

scripts/gdb/linux/pgtable.py

@@ -29,11 +29,9 @@ def page_mask(level=1):
         raise Exception(f'Unknown page level: {level}')
 
 
-#page_offset_base in case CONFIG_DYNAMIC_MEMORY_LAYOUT is disabled
-POB_NO_DYNAMIC_MEM_LAYOUT = '0xffff888000000000'
 def _page_offset_base():
     pob_symbol = gdb.lookup_global_symbol('page_offset_base')
-    pob = pob_symbol.name if pob_symbol else POB_NO_DYNAMIC_MEM_LAYOUT
+    pob = pob_symbol.name
     return gdb.parse_and_eval(pob)