[PATCH 11/26] KVM: PPC: Make RMO a define

[Segher Boessenkool]

>>>> Also, it seems you construct the physical address by masking out  
>>>> bits from
>>>> the effective address.  Most implementations will trap or  
>>>> machine check if
>>>> you address outside of physical address space, instead.
>>>
>>> Well the only case where I remember to have hit a real RMO case  
>>> is on the PS3 - that issues a data/instruction storage interrupt  
>>> when accessing anything > 8MB in real mode.
>>>
>>> So I'd argue this is heavily implementation specific.
>>
>> It is.  So what is the behaviour you want to implement?
>
> The one below.

I'm sorry, I lost it.  "Below"?

>>> Apart from that what I'm trying to cover is that on ppc64  
>>> accessing 0xc0000000000000 in real mode gets you 0x0. Is there a  
>>> better name for this?
>>
>> (You missed two zeroes).
>> In hypervisor real mode, the top few bits are magic.  They are  
>> used for e.g.
>> enabling hypervisor offset real mode.
>> In supervisor real mode, those bits are ignored (and all other  
>> bits that do
>> not correspond to physical address lines may also be ignored).
>
> So which bits exactly are reserved? I couldn't find a reference to  
> that part.

If by "reserved" you mean "cannot be used for addressing", it's the  
top four
bits.  Book III-S chapter 5.7.3 in the Power Architecture 2.06 document.
Implementations are allowed to ignore more bits than that.

I believe in earlier versions of the architecture it was the top two  
bits,
not four, but maybe I misremember.

>> Maybe you want to call it physical_address_mask or similar?
>
> PAM - doesn't sound bad :).

And miraculously nothing in the Power arch uses that acronym yet!  But I
would spell it out if I were you, acronyms are confusing.


Segher