Re: [PATCH] mm/memory_hotplug: fix memmap_on_memory sysfs value retrieval

[David Hildenbrand]

On 10.01.24 15:01, Sumanth Korikkar wrote:
> The set_memmap_mode() function stores the kernel parameter memmap mode
> as an integer. However, the get_memmap_mode() function utilizes
> param_get_bool() to fetch the value as a boolean, leading to potential
> endianness issue. On Big-endian architectures, the memmap_on_memory is
> consistently displayed as 'N' regardless of its actual status.
>
> To address this endianness problem, the solution involves obtaining the
> mode as an integer. This adjustment ensures the proper display of the
> memmap_on_memory parameter, presenting it as one of the following
> options: Force, Y, or N.
>
> Fixes: 2d1f649c7c08 ("mm/memory_hotplug: support memmap_on_memory when memmap is not aligned to pageblocks")
> Suggested-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx> # v6.6+
> Signed-off-by: Sumanth Korikkar <sumanthk@xxxxxxxxxxxxx>
> ---
>   mm/memory_hotplug.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index b944e8bf1911..707027f69150 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -101,9 +101,11 @@ static int set_memmap_mode(const char *val, const struct kernel_param *kp)
>   
>   static int get_memmap_mode(char *buffer, const struct kernel_param *kp)
>   {
> -	if (*((int *)kp->arg) == MEMMAP_ON_MEMORY_FORCE)
> -		return sprintf(buffer,  "force\n");
> -	return param_get_bool(buffer, kp);
> +	int mode = *((int *)kp->arg);
> +
> +	if (mode == MEMMAP_ON_MEMORY_FORCE)
> +		return sprintf(buffer, "force\n");
> +	return sprintf(buffer, "%c\n", mode ? 'Y' : 'N');
>   }

I was wondering if we want to return "Y" instead of "force". But using 
force seems more consistent.

Acked-by: David Hildenbrand <david@xxxxxxxxxx>

--
Cheers,

David / dhildenb