Re: [PATCH v1 1/3] arm64: mm: Fix rodata=full block mapping support for realm guests

[Kevin Brodsky <kevin.brodsky@arm.com>]

On 23/03/2026 14:03, Ryan Roberts wrote:
> [...]
>
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 96711b8578fd0..b9b248d24fd10 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -350,7 +350,6 @@ void __init arch_mm_preinit(void)
>  	}
>  
>  	swiotlb_init(swiotlb, flags);
> -	swiotlb_update_mem_attributes();
>  
>  	/*
>  	 * Check boundaries twice: Some fundamental inconsistencies can be
> @@ -377,6 +376,14 @@ void __init arch_mm_preinit(void)
>  	}
>  }
>  
> +bool page_alloc_available __ro_after_init;
> +
> +void __init mem_init(void)
> +{
> +	page_alloc_available = true;
> +	swiotlb_update_mem_attributes();

The move seems reasonable, x86 calls this function even later (from
arch_cpu_finalize_init()).

> +}
> +
>  void free_initmem(void)
>  {
>  	void *lm_init_begin = lm_alias(__init_begin);
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index a6a00accf4f93..5b6a8d53e64b7 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -773,14 +773,33 @@ int split_kernel_leaf_mapping(unsigned long start, unsigned long end)
>  {
>  	int ret;
>  
> -	/*
> -	 * !BBML2_NOABORT systems should not be trying to change permissions on
> -	 * anything that is not pte-mapped in the first place. Just return early
> -	 * and let the permission change code raise a warning if not already
> -	 * pte-mapped.
> -	 */
> -	if (!system_supports_bbml2_noabort())
> -		return 0;
> +	if (!system_supports_bbml2_noabort()) {
> +		/*
> +		 * !BBML2_NOABORT systems should not be trying to change
> +		 * permissions on anything that is not pte-mapped in the first
> +		 * place. Just return early and let the permission change code
> +		 * raise a warning if not already pte-mapped.
> +		 */
> +		if (system_capabilities_finalized() ||
> +		    !cpu_supports_bbml2_noabort())
> +			return 0;
> +
> +		/*
> +		 * Boot-time: split_kernel_leaf_mapping_locked() allocates from
> +		 * page allocator. Can't split until it's available.
> +		 */
> +		extern bool page_alloc_available;

Could we at least have the declaration in say <asm/mmu.h>? x86 defines a
similar global so we could eventually have a generic global (defined
before mem_init() is called).

Looks good otherwise:

Reviewed-by: Kevin Brodsky <kevin.brodsky@arm.com>

> +		if (WARN_ON(!page_alloc_available))
> +			return -EBUSY;
> +
> +		/*
> +		 * Boot-time: Started secondary cpus but don't know if they
> +		 * support BBML2_NOABORT yet. Can't allow splitting in this
> +		 * window in case they don't.
> +		 */
> +		if (WARN_ON(num_online_cpus() > 1))
> +			return -EBUSY;
> +	}
>  
>  	/*
>  	 * If the region is within a pte-mapped area, there is no need to try to