Re: [PATCH v2 0/1] Fix hmat_adist_nb for CXL

[Alejandro Lucero Palau <alejandro.lucero-palau@amd.com>]

Hi Rafael,


Just a reminder of this fix which, if not applied, could trigger 
problems for the CXL Type2 drivers recently merged in net-next: 
https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=997bfb05c919d2c5ee77c594d354f6c61b99ccdf


As stated in the commit after comments from Richard, this could also be 
a problem for current Type3 CXL kernel support depending on kernel 
configuration.


Let me know if you see any problem with this fix.


Thank you.


On 7/16/26 19:11, alejandro.lucero-palau@amd.com wrote:
> From: Alejandro Lucero <alucerop@amd.com>
>
>   v2:
> 	- Add Fixes (Richarg Cheng)
> 	- Change commit as fix for Type2/Type3 (Richar Cheng)
>
> RFC
> ===
> While working on adding CXL Type2 support I found a problem with
> register_mt_adistance_algorithm() which is used inside
> cxl_region_probe(). It turns out my kernel config had not
> CONFIG_MEMORY_HOTPLUG enabled leading to the hmat_adist_nb notifier
> block deleted after kernel initialization without doing any notifer
> block unregister, leaving the notifier chain unaware of this. A CXL
> Type2 driver can be load after kernel initialization and with a kernel
> not enabling memory hotplug, the notifier registration crashes if the
> released memory from hmat_adist_nb is reused.
>
> I'm not sure but I do not think this can happen for Type3 devices
> because the related CXL driver is used only during kernel initialization
> if memory hotplug not enabled. Type2, aka CXL accelerator drivers, is
> coming and the problem will arise with certainty.
>
> I have contemplated to modify how the identified __meminit and
> __meminitdat are defined in linux/init.h, extending the case for being
> empty definitions if CONFIG_CXL_MEM=y, but I think it makes sense to
> only avoid the use of __meminit for hmat_adist_nb.
>
> FWIW, a Type2 device should not require CONFIG_MEMORY_HOTPLUG and its
> memory is currently initialized by the BIOS. Maybe not having memory
> hotplug enabled is unusual and even more with CXL, so another option
> could be to enable memory hotplug if CXL mem is enabled.
>
> Alejandro Lucero (1):
>    acpi/hmat: preserve hmat_adist_nb notifier block
>
>   drivers/acpi/numa/hmat.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
>
> base-commit: 8cd9520d35a6c38db6567e97dd93b1f11f185dc6