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

[Mahesh Jagannath Salgaonkar]

On 04/03/2018 03:21 PM, Hari Bathini wrote:
> 
> 
> On Monday 02 April 2018 12:00 PM, Mahesh J Salgaonkar wrote:
>> From: Mahesh Salgaonkar <mahesh at 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 at 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.

Yeah, may be we can just move that printk also inside
fadump_memblock_reserve().

Thanks,
-Mahesh.

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