[PATCH] arm64: kdump: fix out of memory issue in __alloc_bootmem_low

[robin.murphy@arm.com (Robin Murphy)]

On 20/05/18 13:20, Chen Zhou wrote:
> From: Mao Wenan <maowenan@huawei.com>
> 
> On arm64 kdump capture kernel, ACPI runtime code and data are outside
> of usable memory range and __alloc_bootmem_low may alloc memory below
> 4G. If we use "crashkernel=Y[@X]" and the start address is above 4G,
> there will be out of memory.
> 
> In this patch, we get max_zone_dma_phys by memblock_start_of_DRAM
> and __pa_symbol(_end).

Entering the crash kernel doesn't magically reconfigure interconnects 
such that 32-bit DMA masters can suddenly address whatever physical 
address range the kernel image happens to be loaded at. This change is 
fundamentally incorrect.

Robin.

> Signed-off-by: Chen Zhou <chenzhou10@huawei.com>
> ---
>   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 1b18b47..df4d212 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -223,7 +223,8 @@ static void __init reserve_elfcorehdr(void)
>    */
>   static phys_addr_t __init max_zone_dma_phys(void)
>   {
> -	phys_addr_t offset = memblock_start_of_DRAM() & GENMASK_ULL(63, 32);
> +	phys_addr_t offset = max(memblock_start_of_DRAM(), __pa_symbol(_end)) &
> +		GENMASK_ULL(63, 32);
>   	return min(offset + (1ULL << 32), memblock_end_of_DRAM());
>   }
>   
>