Re: [PATCH v7 2/4] mm: Introduce memblock_isolate_memory

[Mike Rapoport]

Hi Alexandre,

On Fri, Mar 10, 2023 at 10:45:37AM +0100, Alexandre Ghiti wrote:
> This function allows to split a region in memblock.memory and will be
> useful when setting up the linear mapping with STRICT_KERNEL_RWX: it
> allows to isolate the kernel text/rodata and then avoid to map those
> regions with a PUD/P4D/PGD.
> 
> Signed-off-by: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx>
> ---
>  include/linux/memblock.h |  1 +
>  mm/memblock.c            | 22 +++++++++++++++++++++-
>  2 files changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/memblock.h b/include/linux/memblock.h
> index 50ad19662a32..2f7ef97c0da7 100644
> --- a/include/linux/memblock.h
> +++ b/include/linux/memblock.h
> @@ -125,6 +125,7 @@ int memblock_clear_hotplug(phys_addr_t base, phys_addr_t size);
>  int memblock_mark_mirror(phys_addr_t base, phys_addr_t size);
>  int memblock_mark_nomap(phys_addr_t base, phys_addr_t size);
>  int memblock_clear_nomap(phys_addr_t base, phys_addr_t size);
> +int memblock_isolate_memory(phys_addr_t base, phys_addr_t size);
>  
>  void memblock_free_all(void);
>  void memblock_free(void *ptr, size_t size);
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 25fd0626a9e7..d8cf1c9eccf0 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -753,7 +753,8 @@ static int __init_memblock memblock_isolate_range(struct memblock_type *type,
>  	int idx;
>  	struct memblock_region *rgn;
>  
> -	*start_rgn = *end_rgn = 0;
> +	if (start_rgn && end_rgn)
> +		*start_rgn = *end_rgn = 0;

Generally, it's possible that either start_rgn or end_rgn will be a valid
pointer and this should be handled here and below.

My preference, though would be to leave memblock_isolate_range() as is and
have unused start_rgn and end_rgn in memblock_isolate_memory().

>  
>  	if (!size)
>  		return 0;
> @@ -795,6 +796,9 @@ static int __init_memblock memblock_isolate_range(struct memblock_type *type,
>  					       memblock_get_region_node(rgn),
>  					       rgn->flags);
>  		} else {
> +			if (!end_rgn || !start_rgn)
> +				continue;
> +
>  			/* @rgn is fully contained, record it */
>  			if (!*end_rgn)
>  				*start_rgn = idx;
> @@ -805,6 +809,22 @@ static int __init_memblock memblock_isolate_range(struct memblock_type *type,
>  	return 0;
>  }
>  
> +/**
> + * memblock_isolate_memory - isolate given range from memblock.memory

I think it'd better to use "... range in memblock.memory"

> + * @base: base of range to isolate
> + * @size: size of range to isolate
> + *
> + * Call memblock_isolate_range on memblock.memory to isolate the given range.

Please elaborate that isolate means that the range does not share regions
with other ranges.

> + *
> + * Return:
> + * 0 on success, -errno on failure.
> + */
> +
> +int __init_memblock memblock_isolate_memory(phys_addr_t base, phys_addr_t size)
> +{
> +	return memblock_isolate_range(&memblock.memory, base, size, NULL, NULL);
> +}
> +
>  static int __init_memblock memblock_remove_range(struct memblock_type *type,
>  					  phys_addr_t base, phys_addr_t size)
>  {
> -- 
> 2.37.2
> 

-- 
Sincerely yours,
Mike.