Re: powerpc/fadump: CMA init is failing

[Ritesh Harjani (IBM) <ritesh.list@gmail.com>]

Sourabh Jain <sourabhjain@linux.ibm.com> writes:

> I noticed CMA init for fadump crashkernel memory is failing.
>
> [    0.000000] cma: pageblock_order not yet initialized. Called during 
> early boot?
> [    0.000000] fadump: Failed to init cma area for firmware-assisted 
> dump,-22
>
>
> kernel command-line:
> BOOT_IMAGE=(ieee1275//vdevice/v-scsi@30000070/disk@8100000000000000,msdos2)/vmlinuz-7.0.0-rc1+ 
> root=/dev/mapper/rhel_ltcden3--lp12-root ro 
> rd.lvm.lv=rhel_ltcden3-lp12/root rd.lvm.lv=rhel_ltcden3-lp12/swap 
> fadump=on crashkernel=3G
>
>
> Same issue with kdump CMA reservation:
>
> [    0.000000][    T0] cma: pageblock_order not yet initialized. Called 
> during early boot?

Good that we added those debug prints ;)

I think I know what went wrong, as part of this arch,mm consolidation
patch series [1], I think the order of initialization is changed.

With this patch the new order is ... 
start_kernel()
    - setup_arch()
       - xxx_cma_reserve();
    - mm_core_init_early()
       - free_area_init()
          - sparse_init()
             - set_pageblock_order() // this sets the pageblock_order.

Whereas earlier set_pageblock_order() was called from initmem_init(),
just before cma reservations were being made. 

start_kernel()
    - setup_arch()
       - initmem_init()
         - sparse_init()
           - set_pageblock_order();  // this sets the pageblock_order
       - xxx_cma_reserve();

So that means, pageblock_order is not initialized before these cma
reservation function calls, hence we are seeing these failures.

setup_arch() {
    ...

	/*
	 * Reserve large chunks of memory for use by CMA for kdump, fadump, KVM and
	 * hugetlb. These must be called after initmem_init(), so that
	 * pageblock_order is initialised.
	 */
	fadump_cma_init();
	kdump_cma_reserve();
	kvm_cma_reserve();

    ...
}


So what if we do.. 

start_kernel() {
  ...
	setup_arch(&command_line);
	mm_core_init_early();
    setup_arch_post_mm_core_init(); // and here we call CMA reservation functions ?


References:
[1]: https://lore.kernel.org/linuxppc-dev/20260111082105.290734-1-rppt@kernel.org/T/#m5adf1a845e0a0867066c4f7055f28e6304b73fa5
[2]: https://lore.kernel.org/all/3ae208e48c0d9cefe53d2dc4f593388067405b7d.1729146153.git.ritesh.list@gmail.com/


-ritesh