Re: [PATCH v3 4/7] powerpc/fadump: exclude memory holes while reserving memory in second kernel.

[Hari Bathini <hbathini@linux.vnet.ibm.com>]

On Monday 02 April 2018 12:00 PM, Mahesh J Salgaonkar wrote:
> From: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
>
> The second kernel, during early boot after the crash, reserves rest of
> the memory above boot memory size to make sure it does not touch any of the
> dump memory area. It uses memblock_reserve() that reserves the specified
> memory region irrespective of memory holes present within that region.
> There are chances where previous kernel would have hot removed some of
> its memory leaving memory holes behind. In such cases fadump kernel reports
> incorrect number of reserved pages through arch_reserved_kernel_pages()
> hook causing kernel to hang or panic.
>
> Fix this by excluding memory holes while reserving rest of the memory
> above boot memory size during second kernel boot after crash.
>
> Signed-off-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>
> ---
>   arch/powerpc/kernel/fadump.c |   17 ++++++++++++++++-
>   1 file changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c
> index 011f1aa7abab..a497e9fb93fe 100644
> --- a/arch/powerpc/kernel/fadump.c
> +++ b/arch/powerpc/kernel/fadump.c
> @@ -433,6 +433,21 @@ static inline unsigned long get_fadump_metadata_base(
>   	return be64_to_cpu(fdm->metadata_region.source_address);
>   }
>
> +static void fadump_memblock_reserve(unsigned long base, unsigned long size)
> +{
> +	struct memblock_region *reg;
> +	unsigned long start, end;
> +
> +	for_each_memblock(memory, reg) {
> +		start = max(base, (unsigned long)reg->base);
> +		end = reg->base + reg->size;
> +		end = min(base + size, end);
> +
> +		if (start < end)
> +			memblock_reserve(start, end - start);
> +	}
> +}
> +
>   int __init fadump_reserve_mem(void)
>   {
>   	unsigned long base, size, memory_boundary;
> @@ -487,7 +502,7 @@ int __init fadump_reserve_mem(void)
>   		 */
>   		base = fw_dump.boot_memory_size;
>   		size = memory_boundary - base;
> -		memblock_reserve(base, size);
> +		fadump_memblock_reserve(base, size);
>   		printk(KERN_INFO "Reserved %ldMB of memory at %ldMB "

Mahesh, you may want to change this print as well as it would be 
misleading in case of
holes in the memory.

Thanks
Hari

>   				"for saving crash dump\n",
>   				(unsigned long)(size >> 20),
>