Re: Huawei review of different PMP enhancement schemes

John Hauser

Tariq Kurd wrote:
2. John Hauser's proposal is better than (1)

- the programming model is simpler - it's hard to get my head around
the state changes when setting MML=1, but it's easier to follow

- the modes cover what we need to do

--> Shared executable regions are still missing - I think we also
need to use the W and WX permissions as the PMP enhancement proposal
does (it's not clear if these are reserved or not - they are reserved
in the spreadsheet but not in the document).
Hi Tariq,

I meant for the encodings with W = 1 and R = 0 to continue to be
reserved, as the spreadsheet indicates, but you're right that I forgot
to say so in my document.

I have a different suggestion for adding support for shared executable
regions. I've attached a new spreadsheet file with a new tab showing
my upgraded proposal, version 0.3. You can easily see the changes
by switching between the tabs labeled "4level 0.2" and "4level 0.3".
In my newest version, PMP entries with PL = 0, W = 0, and X = 1
(executable but not writable in S/U mode) are now readable/executable
in M mode. Previously all entries with PL = 0 were readable/writable
for M mode.

When MSL = 3, all PMP entries that give execute permission to M mode
are locked. And new entries that would give execute permission to
M mode cannot be created when MSL = 3, the same as before.

I haven't updated my document yet, but I thought we could debate my
version 0.3 just from the spreadsheet.

I look forward to all feedback.

- John Hauser

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