Re: [PATCH v4 11/15] arm64: mm: Don't abuse memblock NOMAP to check for overlaps

Kevin Brodsky
2026-04-29T13:51:46Z

On 27/04/2026 17:34, Ard Biesheuvel wrote:
> From: Ard Biesheuvel <ardb@kernel.org>
>
> Now that the DRAM mapping routines respect existing table mappings and
> contiguous block and page mappings, it is no longer needed to fiddle
> with the memblock tables to set and clear the NOMAP attribute in order
> to omit text and rodata when creating the linear map.
>
> Instead, map the kernel text and rodata alias first with the desired
> attributes, so that they will not be remapped later with different
> attributes when mapping the memblocks.
>
> Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> ---
> arch/arm64/mm/mmu.c | 24 +++++++-------------
> 1 file changed, 8 insertions(+), 16 deletions(-)
>
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 5e2348b15783..1a4b4337d29a 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1148,12 +1148,15 @@ static void __init map_mem(void)
> flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
>
> /*
> - * Take care not to create a writable alias for the
> - * read-only text and rodata sections of the kernel image.
> - * So temporarily mark them as NOMAP to skip mappings in
> - * the following for-loop
> + * Map the linear alias of the [_text, __init_begin) interval
> + * as non-executable now, and remove the write permission in
> + * mark_linear_text_alias_ro() above (which will be called after
> + * alternative patching has completed). This makes the contents
> + * of the region accessible to subsystems such as hibernate,
> + * but protects it from inadvertent modification or execution.
> */
> - memblock_mark_nomap(kernel_start, kernel_end - kernel_start);
> + __map_memblock(kernel_start, kernel_end, pgprot_tagged(PAGE_KERNEL),

Is it now necessary for that mapping to be tagged? If so, it should
probably be called out in the commit message.

- Kevin

> + flags);
>
> /* map all the memory banks */
> for_each_mem_range(i, &start, &end) {
> @@ -1165,17 +1168,6 @@ static void __init map_mem(void)
> __map_memblock(start, end, pgprot_tagged(PAGE_KERNEL),
> flags);
> }
> -
> - /*
> - * Map the linear alias of the [_text, __init_begin) interval
> - * as non-executable now, and remove the write permission in
> - * mark_linear_text_alias_ro() below (which will be called after
> - * alternative patching has completed). This makes the contents
> - * of the region accessible to subsystems such as hibernate,
> - * but protects it from inadvertent modification or execution.
> - */
> - __map_memblock(kernel_start, kernel_end, PAGE_KERNEL, 0);
> - memblock_clear_nomap(kernel_start, kernel_end - kernel_start);
> }
>
> void mark_rodata_ro(void)