Re: [RFC V2 3/3] s390/mm: Define arch_get_mappable_range()

[Heiko Carstens <hca@linux.ibm.com>]

On Mon, Nov 30, 2020 at 08:59:52AM +0530, Anshuman Khandual wrote:
> This overrides arch_get_mappabble_range() on s390 platform and drops now
> redundant similar check in vmem_add_mapping(). This compensates by adding
> a new check __segment_load() to preserve the existing functionality.
> 
> Cc: Heiko Carstens <hca@linux.ibm.com>
> Cc: Vasily Gorbik <gor@linux.ibm.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: linux-s390@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> ---
>  arch/s390/mm/extmem.c |  5 +++++
>  arch/s390/mm/vmem.c   | 13 +++++++++----
>  2 files changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/s390/mm/extmem.c b/arch/s390/mm/extmem.c
> index 5060956b8e7d..cc055a78f7b6 100644
> --- a/arch/s390/mm/extmem.c
> +++ b/arch/s390/mm/extmem.c
> @@ -337,6 +337,11 @@ __segment_load (char *name, int do_nonshared, unsigned long *addr, unsigned long
>  		goto out_free_resource;
>  	}
>  
> +	if (seg->end + 1 > VMEM_MAX_PHYS || seg->end + 1 < seg->start_addr) {
> +		rc = -ERANGE;
> +		goto out_resource;
> +	}
> +
>  	rc = vmem_add_mapping(seg->start_addr, seg->end - seg->start_addr + 1);
>  	if (rc)
>  		goto out_resource;
> diff --git a/arch/s390/mm/vmem.c b/arch/s390/mm/vmem.c
> index b239f2ba93b0..06dddcc0ce06 100644
> --- a/arch/s390/mm/vmem.c
> +++ b/arch/s390/mm/vmem.c
> @@ -532,14 +532,19 @@ void vmem_remove_mapping(unsigned long start, unsigned long size)
>  	mutex_unlock(&vmem_mutex);
>  }
>  
> +struct range arch_get_mappable_range(void)
> +{
> +	struct range memhp_range;
> +
> +	memhp_range.start = 0;
> +	memhp_range.end =  VMEM_MAX_PHYS;
> +	return memhp_range;
> +}
> +
>  int vmem_add_mapping(unsigned long start, unsigned long size)
>  {
>  	int ret;
>  
> -	if (start + size > VMEM_MAX_PHYS ||
> -	    start + size < start)
> -		return -ERANGE;
> -

I really fail to see how this could be considered an improvement for
s390. Especially I do not like that the (central) range check is now
moved to the caller (__segment_load). Which would mean potential
additional future callers would have to duplicate that code as well.