[RFC PATCH 2/2] powerpc/mm/hash64: Map all the kernel mapping in the same 0xc range

[Michael Ellerman]

Nicholas Piggin <npiggin at gmail.com> writes:
> Aneesh Kumar K.V's on February 19, 2019 4:00 pm:
>> On 2/19/19 11:28 AM, Nicholas Piggin wrote:
>>> Aneesh Kumar K.V's on February 17, 2019 3:16 pm:
>>>> This patch maps vmap, IO and vmemap regions in the 0xc address range
>>>> instead of the current 0xd and 0xf range. This brings the mapping closer
>>>> to radix translation mode.
>>> 
>>> What was the reason for that address layout in the first place?
>>> 
>> 
>> To bring in closer to radix translation mode and it should also help 
>> with KASAN implementation.
>
> No I mean the old implementation. Your change seems fine, it would just
> be good to know what the downside (if any) is from changing. Maybe it 
> was just to make debugging slightly simpler?

I don't know what the reason was for using 0xd to begin with. The
original ppc64 port already had it.

Takes a few seconds to load:
  https://github.com/mpe/linux-fullhistory/commit/c3aa9878533e724f639852c3d951e6a169e04081#diff-0adfdefb64f0f0ef306be06ce7f953ebR173

#define PAGE_OFFSET     0xC000000000000000
#define KERNELBASE      PAGE_OFFSET
#define VMALLOCBASE     0xD000000000000000
#define IOREGIONBASE    0xE000000000000000


cheers