Re: [PATCH] powerpc/mem: Move CMA reservations to arch_mm_preinit

["Dan Horák" <dan@danny.cz>]

Hi Ritesh,

On Sun,  1 Mar 2026 00:17:59 +0530
"Ritesh Harjani (IBM)" <ritesh.list@gmail.com> wrote:

> commit 4267739cabb8 ("arch, mm: consolidate initialization of SPARSE memory model"),
> changed the initialization order of "pageblock_order" from...
> start_kernel()
>     - setup_arch()
>        - initmem_init()
>          - sparse_init()
>            - set_pageblock_order();  // this sets the pageblock_order
>        - xxx_cma_reserve();
> 
> to...
> start_kernel()
>     - setup_arch()
>        - xxx_cma_reserve();
>     - mm_core_init_early()
>        - free_area_init()
>           - sparse_init()
>              - set_pageblock_order() // this sets the pageblock_order.
> 
> So this means, pageblock_order is not initialized before these cma
> reservation function calls, hence we are seeing CMA failures like...
> 
> [    0.000000] kvm_cma_reserve: reserving 3276 MiB for global area
> [    0.000000] cma: pageblock_order not yet initialized. Called during early boot?
> [    0.000000] cma: Failed to reserve 3276 MiB
> ....
> [    0.000000][    T0] cma: pageblock_order not yet initialized. Called during early boot?
> [    0.000000][    T0] cma: Failed to reserve 1024 MiB
> 
> This patch moves these CMA reservations to arch_mm_preinit() which
> happens in mm_core_init() (which happens after pageblock_order is
> initialized), but before the memblock moves the free memory to buddy.
> 
> Fixes: 4267739cabb8 ("arch, mm: consolidate initialization of SPARSE memory model")
> Suggested-by: Mike Rapoport <rppt@kernel.org>
> Reported-and-tested-by: Sourabh Jain <sourabhjain@linux.ibm.com>
> Closes: https://lore.kernel.org/linuxppc-dev/4c338a29-d190-44f3-8874-6cfa0a031f0b@linux.ibm.com/
> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>

awesome, this fixes KVM initialization issues in 7.0-rc. Successfully
started a KVM guest on a Power8 based host system.

...
Mar 10 16:48:11 fedora kernel: NODE_DATA(0) allocated [mem 0x3ff4f9c00-0x3ff50197f]
Mar 10 16:48:11 fedora kernel: kvm_cma_reserve: reserving 819 MiB for global area
Mar 10 16:48:11 fedora kernel: cma: pageblock_order not yet initialized. Called during early boot?
Mar 10 16:48:11 fedora kernel: cma: Failed to reserve 819 MiB
Mar 10 16:48:11 fedora kernel: rfi-flush: ori type flush available
Mar 10 16:48:11 fedora kernel: rfi-flush: patched 12 locations (ori type flush)
...
was the error message in 7.0-rc3


Tested-by: Dan Horák <dan@danny.cz>


		Dan

> ---
>  arch/powerpc/kernel/setup-common.c | 10 ----------
>  arch/powerpc/mm/mem.c              | 14 ++++++++++++++
>  2 files changed, 14 insertions(+), 10 deletions(-)
> 
> --
> 2.53.0
> 
> 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 a985fc96b953..b7982d0243d4 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.