Re: kvm_target, QEMU_KVM_ARM_TARGET_GENERIC_V8 questions

[Peter Maydell <peter.maydell@linaro.org>]

On Thu, 4 Jun 2020 at 17:03, Leif Lindholm <leif@nuviainc.com> wrote:
> But there's also things like:
> - a57_initfn explicitly setting kvm_target, then only being called
>   from max_initfn for !kvm_enabled()

Expected -- a KVM 'max' is nothing to do with a TCG 'max':
 * for KVM, -cpu max means "same as -cpu host"
 * for TCG, -cpu max means "start with an A57, then add in all the
   extra architectural features that have been added since then".

kvm_target being set by a57_initfn is specifically for the case
where a KVM user is using "-cpu cortex-a57".

> - a57_initfn setting cpu->dtb_compatible to "arm,cortex-a57"

What else would it set it to?

> - a57 initfn setting cpu->midr, max_initfn overwriting parts of it

Also expected, TCG's -cpu max is "A57 with lots of extras".

The way we create a TCG -cpu max is a bit odd, as the code was
originally written in a situation where A57 was the most advanced
TCG CPU we had and there were no extra architectural features
supported by our CPU emulation. Today we have an A72 model as
well and a lot of extra architectural features, so the "code
borrowed" to "extras added" ratio looks a bit unbalanced.
Cleaning it up would not be a bad idea.

thanks
-- PMM