Additional AR feedback

[ved-rivos]

Zicfiss will not depend on the A extension (or the Zaamo extension).

At the end of the section named "Zicfiss Instructions Summary", we
suggest adding another paragraph:

If a shadow stack (SS) instruction raises an access-fault,
page-fault, or guest-page-fault exception that is supposed to
indicate the original instruction type (load or store/AMO), then
the reported exception cause is respectively a store/AMO access
fault (code 7), a store/AMO page fault (code 15), or a store/AMO
guest-page fault (code 23).  For shadow stack instructions, the
reported instruction type is always as though it were a store or
AMO, even for instructions SSPOPCHK and C.SSPOPCHK that only read
from memory and do not write to it.

That paragraph can be followed with two non-normative notes, the first
being this:

When Zicfiss is implemented, the existing "store/AMO" exceptions
can be thought of as "store/AMO/SS" exceptions, indicating that the
trapping instruction is either a store, an AMO, or a shadow stack
instruction.

The second note is:

The H (hypervisor) extension specifies that when a guest-page
fault is caused by an implicit memory access of VS-stage address
translation, the reported exception is either a load or store/AMO
guest-page fault based not on the original instruction type
but rather on whether the memory access attempted for VS-stage
translation was a read or a write of memory.  VS-stage address
translation can thus cause a shadow stack instruction to raise
a load guest-page-fault exception.

The SSAMOSWAP instructions require memory attribute AMOSwap, the same
as the regular AMOSWAP instructions.

Please replace "single- and first-stage page tables" with "single-stage
and VS-stage page tables".

To avoid yet another special case, we propose that SSAMOSWAP can work
with mstatus.MPRV = 1. Hence, in this sentence,

At privilege mode M, any memory access by an SSAMOSWAP instruction
will result in a store/AMO access-fault exception.

replace "At privilege mode M" with "When the effective privilege mode
is M".

[ved-rivos]

PR #184 addresses 1 through 4. Item 5 was previously addressed in PR #182

[ved-rivos]

Merging the PR for readability. Please leave feedback in the PR or in this issue.