Re: [PATCH v3 2/8] arm64: Add support for MEMBLOCK_PTEMAP

[Mike Rapoport <rppt@kernel.org>]

On Wed, Nov 11, 2026 at 11:07:32AM +0000, Vincent Donnefort wrote:
> With the MEMBLOCK_PTEMAP flag, force a PTE-level mapping. This also

I'd expand this to "Force a PTE-level mapping for memblock regions with
MEMBLOCK_PTEMAP flag set".

> disables contiguous PTEs to make sure any page from the memblock can be

                                     and memblock region here ^

> safely unmapped from the linear map.
> 
> Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
> ---
>  arch/arm64/mm/mmu.c | 22 +++++++++++++++-------
>  1 file changed, 15 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 140520b351e2..a4cafafa1d82 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -1184,9 +1184,8 @@ static void __init map_mem(void)
>  	phys_addr_t init_begin = __pa_symbol(__init_begin);
>  	phys_addr_t init_end = __pa_symbol(__init_end);
>  	phys_addr_t kernel_end = __pa_symbol(__bss_stop);
> -	phys_addr_t start, end;
>  	int flags = NO_EXEC_MAPPINGS;
> -	u64 i;
> +	struct memblock_region *r;
>  
>  	/*
>  	 * Setting hierarchical PXNTable attributes on table entries covering
> @@ -1226,9 +1225,14 @@ static void __init map_mem(void)
>  		       flags);
>  
>  	/* map all the memory banks */
> -	for_each_mem_range(i, &start, &end) {
> +	for_each_mem_region(r) {
> +		phys_addr_t start, end;
> +		int rflags = flags;
> +
> +		if (memblock_is_nomap(r))
> +			continue;
>  		/*
> -		 * for_each_mem_range may return sub-page-aligned boundaries
> +		 * for_each_mem_region may return sub-page-aligned boundaries
>  		 * after memblock_mark_nomap() splits regions at byte precision.
>  		 * __create_pgd_mapping_locked aligns phys down to PAGE_MASK,
>  		 * which could accidentally map no-map memory on the boundary.
> @@ -1237,17 +1241,21 @@ static void __init map_mem(void)
>  		 * regions. The cost is at most one page of unmapped gap at
>  		 * each boundary.
>  		 */
> -		start = PAGE_ALIGN(start);
> -		end = end & PAGE_MASK;
> +		start = PAGE_ALIGN(r->base);
> +		end = (r->base + r->size) & PAGE_MASK;

Nit: as we anyway change the assignment to end, PAGE_ALIGN_DOWN() is
slightly more explicit.

>  		if (start >= end)
>  			continue;
> +
> +		if (memblock_is_ptemap(r))
> +			rflags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
> +
>  		/*
>  		 * The linear map must allow allocation tags reading/writing
>  		 * if MTE is present. Otherwise, it has the same attributes as
>  		 * PAGE_KERNEL.
>  		 */
>  		__map_memblock(start, end, pgprot_tagged(PAGE_KERNEL),
> -			       flags);
> +			       rflags);
>  	}
>  }
>  
> -- 
> 2.56.0.542.g3ef89b7020-goog
> 

-- 
Sincerely yours,
Mike.