Re: powerpc/fadump: CMA init is failing

[Sourabh Jain <sourabhjain@linux.ibm.com>]

Hello Ritesh,

On 28/02/26 08:05, Ritesh Harjani (IBM) wrote:
> Mike Rapoport <rppt@kernel.org> writes:
>
>> Hi Ritesh,
>>
>> On Fri, Feb 27, 2026 at 10:39:53PM +0530, Ritesh Harjani wrote:
>>> 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 ?
>>   
>> Unless I'm missing something these cma reservations can be moved to
>> arch_mm_preinit().
>> It runs after mm_core_init_early() and before memblock moves the free
>> memory to the buddy.
>>
> Right. I think, we should be able to use that...
>
> @Sourabh,
>
> I don't have access to the systems (travelling back...). Could you
> please give this a try?
>
>
> diff --git a/arch/powerpc/kernel/setup-common.c b/arch/powerpc/kernel/setup-common.c
> index cb5b73adc250..b1761909c23f 100644
> --- a/arch/powerpc/kernel/setup-common.c
> +++ b/arch/powerpc/kernel/setup-common.c
> @@ -35,7 +35,6 @@
>   #include <linux/of_irq.h>
>   #include <linux/hugetlb.h>
>   #include <linux/pgtable.h>
> -#include <asm/kexec.h>
>   #include <asm/io.h>
>   #include <asm/paca.h>
>   #include <asm/processor.h>
> @@ -995,15 +994,6 @@ void __init setup_arch(char **cmdline_p)
>   
>   	initmem_init();
>   
> -	/*
> -	 * 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();
> -
>   	early_memtest(min_low_pfn << PAGE_SHIFT, max_low_pfn << PAGE_SHIFT);
>   
>   	if (ppc_md.setup_arch)
> diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
> index 29bf347f6012..5ba947e4fe37 100644
> --- a/arch/powerpc/mm/mem.c
> +++ b/arch/powerpc/mm/mem.c
> @@ -30,6 +30,10 @@
>   #include <asm/setup.h>
>   #include <asm/fixmap.h>
>   
> +#include <asm/fadump.h>
> +#include <asm/kexec.h>
> +#include <asm/kvm_ppc.h>
> +
>   #include <mm/mmu_decl.h>
>   
>   unsigned long long memory_limit __initdata;
> @@ -268,6 +272,16 @@ void __init paging_init(void)
>   
>   void __init arch_mm_preinit(void)
>   {
> +
> +	/*
> +	 * Reserve large chunks of memory for use by CMA for kdump, fadump, KVM
> +	 * and hugetlb. These must be called after pageblock_order is
> +	 * initialised.
> +	 */
> +	fadump_cma_init();
> +	kdump_cma_reserve();
> +	kvm_cma_reserve();
> +
>   	/*
>   	 * book3s is limited to 16 page sizes due to encoding this in
>   	 * a 4-bit field for slices.

The above changes fix the issue. CMA initialization now works for both 
kdump and fadump.

Thanks for the fix.

- Sourabh Jain