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List:       kvm-ppc
Subject:    Re: [PATCH 11/26] KVM: PPC: Make RMO a define
From:       Alexander Graf <agraf () suse ! de>
Date:       2010-06-29 8:04:44
Message-ID: 7504F7A1-C394-4037-A951-A9AC724C0809 () suse ! de
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On 29.06.2010, at 09:52, Segher Boessenkool wrote:

> > > > > 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"?

Well, the ones a few lines 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.

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

> 
> > > 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.

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

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