Re: [RFC PATCH 09/16] KVM: arm64: Allow ID registers to by dynamically read-as-zero

Peter Maydell
2018-08-08T14:03:53Z

On 8 August 2018 at 10:11, Dave Martin <Dave.Martin@arm.com> wrote:
> At its heart, I'm trying to abstract out the special behaviour of
> all unallocated ID registers, so that we can decide at runtime which
> ones to hide fro the guest: within the ID register block, each
> unallocated register becomes RAZ, not UNDEFINED as would be the case
> for other system registers, so we need to capture both behaviours.

I think a better way to think of the ID register block is
that all the registers in it *are* allocated. It's just that
some of them are specified as RAZ/WI (because no bits in
them have been given meaning yet). Then you retain the
straightforward "unallocated == UNDEF". (In the Arm ARM
the gaps in the ID register block are documented as
"reserved, RAZ", not "unallocated".)

thanks
-- PMM