On 06/13/22 at 04:09pm, Zhen Lei wrote:
> For crashkernel=X without '@offset', select a region within DMA zones
> first, and fall back to reserve region above DMA zones. This allows
> users to use the same configuration on multiple platforms.

LGTM,

Acked-by: Baoquan He <b...@redhat.com>

> 
> Signed-off-by: Zhen Lei <thunder.leiz...@huawei.com>
> ---
>  Documentation/admin-guide/kernel-parameters.txt |  2 +-
>  arch/arm64/mm/init.c                            | 16 +++++++++++++++-
>  2 files changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt 
> b/Documentation/admin-guide/kernel-parameters.txt
> index 61b179232b68001..fdac18beba5624e 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -823,7 +823,7 @@
>                       memory region [offset, offset + size] for that kernel
>                       image. If '@offset' is omitted, then a suitable offset
>                       is selected automatically.
> -                     [KNL, X86-64] Select a region under 4G first, and
> +                     [KNL, X86-64, ARM64] Select a region under 4G first, and
>                       fall back to reserve region above 4G when '@offset'
>                       hasn't been specified.
>                       See Documentation/admin-guide/kdump/kdump.rst for 
> further details.
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 5390f361208ccf7..8539598f9e58b4d 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -138,6 +138,7 @@ static void __init reserve_crashkernel(void)
>       unsigned long long crash_max = CRASH_ADDR_LOW_MAX;
>       char *cmdline = boot_command_line;
>       int ret;
> +     bool fixed_base;
>  
>       if (!IS_ENABLED(CONFIG_KEXEC_CORE))
>               return;
> @@ -166,15 +167,28 @@ static void __init reserve_crashkernel(void)
>               return;
>       }
>  
> +     fixed_base = !!crash_base;
>       crash_size = PAGE_ALIGN(crash_size);
>  
>       /* User specifies base address explicitly. */
> -     if (crash_base)
> +     if (fixed_base)
>               crash_max = crash_base + crash_size;
>  
> +retry:
>       crash_base = memblock_phys_alloc_range(crash_size, CRASH_ALIGN,
>                                              crash_base, crash_max);
>       if (!crash_base) {
> +             /*
> +              * Attempt to fully allocate low memory failed, fall back
> +              * to high memory, the minimum required low memory will be
> +              * reserved later.
> +              */
> +             if (!fixed_base && (crash_max == CRASH_ADDR_LOW_MAX)) {
> +                     crash_max = CRASH_ADDR_HIGH_MAX;
> +                     crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
> +                     goto retry;
> +             }
> +
>               pr_warn("cannot allocate crashkernel (size:0x%llx)\n",
>                       crash_size);
>               return;
> -- 
> 2.25.1
> 


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