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

On 29.06.2010, at 09:52, Segher Boessenkool wrote:

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Also, it seems you construct the physical address by masking out =

bits from

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the effective address.  Most implementations will trap or machine =

check if

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you address outside of physical address space, instead.

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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.

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So I'd argue this is heavily implementation specific.

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It is.  So what is the behaviour you want to implement?

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The one below.

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

Well, the ones a few lines below :).

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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?

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(You missed two zeroes).
In hypervisor real mode, the top few bits are magic.  They are used =

for e.g.

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enabling hypervisor offset real mode.
In supervisor real mode, those bits are ignored (and all other bits =

that do

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not correspond to physical address lines may also be ignored).

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So which bits exactly are reserved? I couldn't find a reference to =

that part.

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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.
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I believe in earlier versions of the architecture it was the top two =

bits,

not four, but maybe I misremember.

Ah, nice. So that part is implementation specific too. Awesome ;).

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Maybe you want to call it physical_address_mask or similar?

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PAM - doesn't sound bad :).

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And miraculously nothing in the Power arch uses that acronym yet!  But =

I

would spell it out if I were you, acronyms are confusing.

Well, the bad thing about not using acronyms here is that I'll run out =
of the 80 character limit pretty soon. And that means line wraps and =
more confusingness when reading the code.

Alex