On Fri, Jul 30, 2021 at 9:18 AM Marc Zyngier [off-list ref] wrote:

You want the ARM FVP model, or maybe even the Foundation model. It has
support all the way to ARMv8.7 apparently. I personally use the FVP,
get in touch offline and I'll help you with the setup.

In general, I tend to trust the ARM models a lot more than QEMU for
the quality of the emulation. You can tune it in some bizarre way
(the cache modelling is terrifying), and it will definitely do all
kind of crazy reordering and speculation.

Awesome, thanks. I'll give this a try.

quoted

quoted

I really dislike the fallback to !vhe here. I'd rather you
special-case the emulated ptimer in the VHE case:

        if (has_vhe()) {
                map->direct_vtimer = vcpu_vtimer(vcpu);
                if (!timer_get_offset(vcpu_ptimer(vcpu)))
                        map->direct_ptimer = vcpu_ptimer(vcpu);
                        map->emul_ptimer = NULL;
                } else {
                        map->direct_ptimer = NULL;
                        map->emul_ptimer = vcpu_ptimer(vcpu);
                }
        } else {

Ack.

quoted

and you can drop the timer_emulation_required() helper which doesn't
serve any purpose.

Especially if I add ECV to this series, I'd prefer to carry it than
open-code the check for CNTPOFF && !ECV in get_timer_map(). Do you
concur? I can tighten it to ptimer_emulation_required() and avoid
taking an arch_timer context if you prefer.

Sure, whatever you prefer. I'm not set on one way or another, but in
the above case, it was clearly easier to get rid of the helper.

Agreed, it made sense to prune before.

There has been a trap, so that already was a context synchronisation
event. but it would be pretty common for the counter to be speculated
way early, when entering EL2. That's not the end of the world, but
that's not an accurate emulation. You'd want it to be as close as
possible to the reentry point into the guest.

Cool, I'll add the barrier to kick the can closer to guest entry.

--
Thanks,
Oliver

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