Re: [PATCH 2/2] arm64: mm: fix kdump broken with ZONE_DMA reintroduced

[Nicolas Saenz Julienne]

Hi Chen, thanks for looking at this.

On Sat, 2020-12-26 at 11:35 +0800, Chen Zhou wrote:
> If the memory reserved for crash dump kernel falled in ZONE_DMA32,
> the devices in crash dump kernel need to use ZONE_DMA will alloc fail.
> 
> Fix this by reserving low memory in ZONE_DMA if CONFIG_ZONE_DMA is
> enabled, otherwise, reserving in ZONE_DMA32.
> 
> Fixes: bff3b04460a8 ("arm64: mm: reserve CMA and crashkernel in ZONE_DMA32")

I'm not so sure this counts as a fix, if someone backports it it'll probably
break things as it depends on the series that dynamically sizes DMA zones.

> Signed-off-by: Chen Zhou <chenzhou10@xxxxxxxxxx>
> ---

Why not doing the same with CMA? You'll probably have to move the
dma_contiguous_reserve() call into bootmem_init() so as to make sure that
arm64_dma_phys_limit is populated.

Regards,
Nicolas

>  arch/arm64/mm/init.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 7b9809e39927..5074e945f1a6 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -85,7 +85,8 @@ static void __init reserve_crashkernel(void)
>  
> 
>  	if (crash_base == 0) {
>  		/* Current arm64 boot protocol requires 2MB alignment */
> -		crash_base = memblock_find_in_range(0, arm64_dma32_phys_limit,
> +		crash_base = memblock_find_in_range(0,
> +				arm64_dma_phys_limit ? : arm64_dma32_phys_limit,
>  				crash_size, SZ_2M);
>  		if (crash_base == 0) {
>  			pr_warn("cannot allocate crashkernel (size:0x%llx)\n",

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