Re: comments on PMP enhancements

John Hauser

Hi Allen,

Since it looks like you're responding to me, I'll try to answer.

Two quick comments:
- I am assuming that this is a proposal to replace the existing "enhanced"
PMP proposal, rather than an "enhanced-enhanced" PMP proposal.
There are now three proposals that I know of. The original and most
visible is the task group's working proposal, which you already know.
The only version I've seen is here:

As part of my feedback, I suggested a modified proposal with four
"security levels". To make this more accessible, I've now created a
simple PDF document, which can be found here:

As the document explains, my top-most security level (what I'm now
calling "full security") is for all practical purposes the same as the
task group's proposal when MML = 1. The important difference is that
I offer two "proto-security" levels that provide better protection than
you get with MML = 0, which is the only alternative to "full security"
under the task group's working proposal. I would be pleased if you
could give my proposal a look and give me your thoughts.

Tariq Kurd has been developing a different modified proposal. I need
to review his latest version, but when I last looked, it appeared to me
to satisify the needs of his system in a slightly more complex way than
my proposal, without any advantage. Hence, I confess I haven't yet
seen the appeal. I'll try again.

- do we ever need to allow Write_Only and Write&Execute regions? OR can we
continue to disallow them,
Though I neglected to say so in my document, I meant for these
combinations to continue to be reserved encodings. If anyone is
proposing write-only or write/execute permissions, I'm not yet aware of

except for the specific shared RW/RO regions
defined by the enhanced proposal
( which in this case is when MML=1, M=0 as opposed to the enhanced
proposal of MML=1, L=0)
This sounds like Mr, Kurd's proposal, not mine.

Separately, there is a proposal to have an S-PMP, which further filters
addresses but allows Smode to configure them.
It would be useeful to consider whether they would be completely separate
CSRs or they could overlay the existing ones ones somehow.
Even if they are totally separate, it would be useful to ensure the
encodings were similar enough that the same HW (with simple external wiring
changes) would work for both.
I totally agree. Haven't looked at it yet, though.


- John Hauser

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