Subject: Re: [PATCH v3 02/11] s390x/mm: Fail when an altmap is used for arch_add_memory()

From: Michal Hocko <[email-masked]>
Date: Mon, 1 Jul 2019 09:43:06 +0200

On Mon 27-05-19 13:11:43, David Hildenbrand wrote:
> ZONE_DEVICE is not yet supported, fail if an altmap is passed, so we
> don't forget arch_add_memory()/arch_remove_memory() when unlocking
> support.

Why do we need this? Sure ZONE_DEVICE is not supported for s390 and so
might be the case for other arches which support hotplug. I do not see
much point in adding warning to each of them.

> Cc: Martin Schwidefsky <[email-masked]>
> Cc: Heiko Carstens <[email-masked]>
> Cc: Andrew Morton <[email-masked]>
> Cc: Michal Hocko <[email-masked]>
> Cc: Mike Rapoport <[email-masked]>
> Cc: David Hildenbrand <[email-masked]>
> Cc: Vasily Gorbik <[email-masked]>
> Cc: Oscar Salvador <[email-masked]>
> Suggested-by: Dan Williams <[email-masked]>
> Signed-off-by: David Hildenbrand <[email-masked]>
> ---
>  arch/s390/mm/init.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
> index 14d1eae9fe43..d552e330fbcc 100644
> --- a/arch/s390/mm/init.c
> +++ b/arch/s390/mm/init.c
> @@ -226,6 +226,9 @@ int arch_add_memory(int nid, u64 start, u64 size,
>  	unsigned long size_pages = PFN_DOWN(size);
>  	int rc;
>  
> +	if (WARN_ON_ONCE(restrictions->altmap))
> +		return -EINVAL;
> +
>  	rc = vmem_add_mapping(start, size);
>  	if (rc)
>  		return rc;
> -- 
> 2.20.1
> 

-- 
Michal Hocko
SUSE Labs