Re: [PATCH v3 41/42] target/arm: Implement FEAT_HAFDBS

[Peter Maydell]

On Fri, 7 Oct 2022 at 14:47, Peter Maydell <peter.maydell@linaro.org> wrote:
> Do we really need to go all the way back to restart_atomic_update?

> Are we allowed to do the access and dirty bit updates with separate
> atomic accesses?

I've just discovered that the latest revision of the Arm ARM (rev I.a)
is clearer on this -- R_SGJBL and I_YZSVV clearly say that we need to
go back to restart_atomic_update for dirty bit updates, and it's a
reasonable assumption that this is true also for atomic updates.
And R_PRHKD says you're permitted to do everything in one rmw,
which clearly implies that you're permitted also not to. And if
you restart the descriptor handling it's architecturally not
distinguishable whether you did one rmw or two. So both of these
are fine the way you have them in your patch.

thanks
-- PMM