On 29.06.2010, at 09:32, Segher Boessenkool wrote:

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On PowerPC it's very normal to not support all of the physical RAM =

in real mode.

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Oh?  Are you referring to "real mode limit", or 32-bit =

implementations with

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more than 32 address lines, or something else?

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The former.

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Okay.  In that case, the hypervisor can usually access all of physical
ram directly, unless it limits itself; and a supervisor gets either
no real mode access, or all ram, or some part -- whatever the =

hypervisor

likes.
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If you access outside of ram, you will most likely get a machine =

check.

Depends on the implementation (like most things here).
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Either way, RMO is a really bad name for this, since that name is =

already

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used for a similar but different concept.

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It's the same concept, no? Not all physical memory is accessible from =

real mode.

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I think you're looking for "real mode limit":
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The concept is called "offset real mode".
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RMO ("real mode offset") is the value that is ORed to an effective =

address

to make the physical address (not added, "offset" is a pretty bad =

name).

RML ("real mode limit") is the value that has to be bigger than the =

effective

address or you will get an exception.
RMA ("real mode area") is the name for the range of addresses usable =

in offset

real mode.
=20

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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?

The one 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.

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.

Maybe you want to call it physical_address_mask or similar?

PAM - doesn't sound bad :).


Alex