Re: [PATCHv2 1/3] x86/64/mm: Always use dynamic memory layout

[Ard Biesheuvel <ardb@kernel.org>]

On Fri, 16 May 2025 at 10:15, Kirill A. Shutemov
<kirill.shutemov@linux.intel.com> wrote:
>
> 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>

Reviewed-by: Ard Biesheuvel <ardb@kernel.org>

> ---
>  arch/x86/Kconfig                        | 8 --------
>  arch/x86/include/asm/page_64_types.h    | 4 ----
>  arch/x86/include/asm/pgtable_64_types.h | 6 ------
>  arch/x86/kernel/head64.c                | 2 --
>  scripts/gdb/linux/pgtable.py            | 4 +---
>  5 files changed, 1 insertion(+), 23 deletions(-)
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 891a69b308cb..d3c2da3b2f0b 100644
> --- a/arch/x86/Kconfig
> +++ b/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
> @@ -2167,17 +2166,10 @@ 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
> diff --git a/arch/x86/include/asm/page_64_types.h b/arch/x86/include/asm/page_64_types.h
> index 1faa8f88850a..6b8c8169c71d 100644
> --- a/arch/x86/include/asm/page_64_types.h
> +++ b/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)
>
> diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
> index e83721db18c9..eee06f77b245 100644
> --- a/arch/x86/include/asm/pgtable_64_types.h
> +++ b/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
> diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
> index 14f7dda20954..9f617be64fa9 100644
> --- a/arch/x86/kernel/head64.c
> +++ b/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)
> diff --git a/scripts/gdb/linux/pgtable.py b/scripts/gdb/linux/pgtable.py
> index 30d837f3dfae..09aac2421fb8 100644
> --- a/scripts/gdb/linux/pgtable.py
> +++ b/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)
>
>
> --
> 2.47.2
>
>