Re: [PATCH 2/3] mm/memory_hotplug: Allow arch override of non boot memory resource names

[David Hildenbrand <david@redhat.com>]

On 26.03.20 19:07, James Morse wrote:
> Memory added to the system by hotplug has a 'System RAM' resource created
> for it. This is exposed to user-space via /proc/iomem.
> 
> This poses problems for kexec on arm64. If kexec decides to place the
> kernel in one of these newly onlined regions, the new kernel will find
> itself booting from a region not described as memory in the firmware
> tables.
> 
> Arm64 doesn't have a structure like the e820 memory map that can be
> re-written when memory is brought online. Instead arm64 uses the UEFI
> memory map, or the memory node from the DT, sometimes both. We never
> rewrite these.
> 
> Allow an architecture to specify a different name for these hotplug
> regions.
> 
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
>  mm/memory_hotplug.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 0a54ffac8c68..69b03dd7fc74 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -42,6 +42,10 @@
>  #include "internal.h"
>  #include "shuffle.h"
>  
> +#ifndef MEMORY_HOTPLUG_RES_NAME
> +#define MEMORY_HOTPLUG_RES_NAME "System RAM"
> +#endif

So I assume changing this for all architectures would result in some
user space tool breaking? Are we aware of any?

I do wonder if we should simply change it for all architectures if possible.


> +
>  /*
>   * online_page_callback contains pointer to current page onlining function.
>   * Initially it is generic_online_page(). If it is required it could be
> @@ -103,7 +107,7 @@ static struct resource *register_memory_resource(u64 start, u64 size)
>  {
>  	struct resource *res;
>  	unsigned long flags =  IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
> -	char *resource_name = "System RAM";
> +	char *resource_name = MEMORY_HOTPLUG_RES_NAME;
>  
>  	if (start + size > max_mem_size)
>  		return ERR_PTR(-E2BIG);
> 


-- 
Thanks,

David / dhildenb