[PATCH v2] powerpc: increase MIN RMA size for CAS negotiation

[Sourabh Jain]

Hello Michael,

On 07/12/24 07:28, Michael Ellerman wrote:
> Avnish Chouhan <avnish at linux.ibm.com> writes:
>> Change RMA size from 512 MB to 768 MB which will result
>> in more RMA at boot time for PowerPC.
> Did you consider just increasing it to 1GB?

I see an impact of setting RMA to 1GB on fadump. Here’s how:

The minimum reservation recommended by us for fadump is 768MB.
In this case, the boot_mem_top in fadump.c will be 768MB, and the
memory reservation for fadump will start from a 768MB offset.

Now, let’s say the production kernel crashes, and the firmware copies
the 0–768MB region to the fadump reserved area and boots the fadump
kernel to capture the dump.

If RMA is set to 1GB, it will allow GRUB to use memory up to 1GB. In such
a case, there is a possibility that GRUB could corrupt the fadump 
reserved area.

Thanks,
Sourabh Jain