Re: [PATCH] exec: Add RISC-V WorldGuard WID field to MemTxAttrs

On Fri, 17 Jul 2026 at 11:08, Alex Bennée <[email protected]> wrote:
>
> Philippe Mathieu-Daudé <[email protected]> writes:
>
> > On 18/3/26 05:40, Jim Shu wrote:
> >> On Tue, Feb 10, 2026 at 8:25 AM Richard Henderson
> >> <[email protected]> wrote:
> >> ...
> >>> Hmm.  This really overlaps the secure and space fields from arm, and possibly some of the
> >>> others as well (e.g. user, requester_id, pid).
> >>>
> >>> I don't really have a good suggestion for that right now, but it would be nice to not keep
> >>> expanding the count of these sorts of fields that somehow specify the originator, but
> >>> clearly cannot overlap.
> >>>
> >>> I'm reasonably sure we've had this discussion before, but nothing has come of it.
> >>>
> >>> Time to paint the bikeshed again?
> >
> > Last discussion IIRC:
> > https://lore.kernel.org/qemu-devel/CAFEAcA8vKNkfKgp_Yymo9NA1=E2XJYXAMTgO3z6q6DHgqkAwRw@mail.gmail.com/
> >
> > (see also a suggestion in
> > https://lore.kernel.org/qemu-devel/[email protected]/)
>
> Also somewhat related:
>
>   Message-Id: <[email protected]>
>   Date: Fri, 11 Nov 2022 18:25:15 +0000
>   Subject: [PATCH for 8.0 v5 00/20] use MemTxAttrs to avoid current_cpu in hw/
>
> Another case that was mentioned in a Core Collective meeting was
> handling MMIO devices with IOMMUs (currently requester_id is tied to
> PCI). I guess the WorldGuard WID field is a similar thing.

The worldguard ID is more like the Arm security space field, as I
understand it -- it encodes what the request should or should
not be able to access, and multiple different transaction masters
might be able to send with the same worldguard ID. A requester_id
on the other hand is intended to identify a unique sender.
(In AXI these things turn up in different signals.)

I think the trick with requester_id is that we need to identify
what we need to encode here and make sure we don't confuse things.
(e.g. a CPU needs to not be able to emit something that looks like
a PCI request by accident, because some devices need to be able
to tell "this really did come from a PCI device" from "this is a
CPU doing a normal load/store insn"). So we probably want some
kind of "this is what the requester_id is" enum rather than just
a convention.

thanks
-- PMM