[Libre-soc-dev] Wishbone and House Contract Of Sale Proposition

[Jacob Lifshay]

On Thu, Oct 28, 2021, 17:11 lkcl <luke.leighton at gmail.com> wrote:

> this is unavoidable except for architectures like The Mill which are fully
> timing-predictable (100% fixed timing) so much so that the compiler can do
> the entire static allocation at compiletime, in fact that is literally the
> entire point of the Mill.
>

the Mill is not 100% static timing predictable, since there are still cache
misses/hits that take different amounts of time.

>
> (and look how much work had gone into the Mill llvm compiler, and binaries
> are not portable)
>
> the only other way to avoid timing info leak is to massively oversubscribe
> backend Function Units and internal buses so badly that at no time and
> under no circumstances will any instruction issue ever stall or result in
> any kind of resource contention, not for memory, not for cache, not for
> TLB, not for Virtual Memory, not for pipelines, not for Reservation
> Stations, not for regfile ports, not for SMP, nothing.
>
> this is of course absolutely hopelessly unrealistic but it is what it
> takes to ensure zero timing leaks.


Actually, the spectre-proof idea I came up with doesn't require
oversubscription at all...the cpu stays mostly unmodified and still should
be about as fast/power-efficient/etc.

https://bugs.libre-soc.org/show_bug.cgi?id=209

Jacob