Re: [RFC PATCH v1 1/1] acpi/hmat: preserve hmat_adist_nb notifier block

[Richard Cheng <icheng@nvidia.com>]

On Tue, Jun 30, 2026 at 03:35:07PM +0800, alejandro.lucero-palau@amd.com wrote:
> From: Alejandro Lucero <alucerop@amd.com>
> 
> Remove __meminitdata from hmat_adist_nb declaration preserving it even
> when CONFIG_MEMORY_HOTPLUG is not set. Otherwise further notifier
> registrations using register_mt_adistance_algorithm() will find a
> notifier chain likely corrupted. This is the case when a CXL Type2
> driver will load after kernel initialization and a CXL region created from
> its committed HDM decoders registers an mt_adistance_algorithm notifier.
> 
> Signed-off-by: Alejandro Lucero <alucerop@amd.com>
> ---
>  drivers/acpi/numa/hmat.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/acpi/numa/hmat.c b/drivers/acpi/numa/hmat.c
> index 9792dc394756..3006789ae31f 100644
> --- a/drivers/acpi/numa/hmat.c
> +++ b/drivers/acpi/numa/hmat.c
> @@ -995,7 +995,7 @@ static int hmat_calculate_adistance(struct notifier_block *self,
>  	return NOTIFY_STOP;
>  }
>  
> -static struct notifier_block hmat_adist_nb __meminitdata = {
> +static struct notifier_block hmat_adist_nb = {
>  	.notifier_call = hmat_calculate_adistance,
>  	.priority = 100,
>  };
> -- 
> 2.34.1
> 
>

I think this is not limited to CXL type 2 device.
cxl_region_probe() already calls register_mt_adistance_algorithm(), and CXL_REGION
depends only on SPARSEMEM, not MEMORY_HOTPLUG, so with NUMA=y, MEMORY_HOTPLUG=n, CXL_ACPI=y and CXL_REGION=y,
any runtime CXL region probe walks the chain. I would suggest some tweak for commit message.
Also adding Fixes: 3718c02dbd4c ("acpi, hmat: calculate abstract distance with HMAT")

And maybe keep unconditional removal rather than a consumer-keyed attribute.
register_mt_adistance_algorithm() is callable by any runtime module,
not just CXL, so a CONFIG_CXL_MEM-keyed condition would  still leave the hole
for other callers.

What do you think ?

Best regards,
Richard Cheng.