comments on PMP enhancements
First, as we all know, the existing PMP standard allows PMP entries toAllen Baum:
You need to be careful with terminology. I am assuming thatSorry, I meant that, under the existing standard, locked PMP entries
are intended to deny some or all accesses from M mode to a memory
region. The RISC-V standard says, "In addition to locking the PMP
entry, the L bit indicates whether the R/W/X permissions are enforced
on M-mode accesses." The only reason the entry is locked is so that
M mode can't then undo this restriction imposed on it.
But: if an entry is created (necessarily by M-mode) that is locked and suchSuch an entry is impossible under the existing standard. There's no
way to encode it.
And, evenAs I said to Jonathan Behrens, locked regions always have to be at the
head of the table to be effective. Ordinarily, there won't be any
unlocked regions of higher priority.
It feels like you've misunderstood the role of locked PMP entries under
the existing standard, and that's why you didn't understand my point.
Or you missed the significance I intended with my words "the existing
PMP standard allows ...."
- John Hauser