Re: [RFC v12 17/65] target/arm: tcg: add stubs for some helpers for non-tcg builds

[Richard Henderson]

On 4/8/21 3:39 AM, Claudio Fontana wrote:
> On 3/28/21 6:22 PM, Richard Henderson wrote:
> > On 3/26/21 1:36 PM, Claudio Fontana wrote:
> > > +int fp_exception_el(CPUARMState *env, int cur_el)
> > > +{
> > > +    return 0;
> > > +}
> >
> > Oh, I'm pretty sure this should be identical with sve_exception_el, where the
> > fpu may or may not be enabled for a given cpu state (e.g. lazy fpu switching in
> > the kvm guest kernel).
> >
> > Are we really returning constant 0 for kvm before your patch set?
> >
> >
> > r~
>
> I tried to remember and follow the fp_exception_el in detail,
> and _maybe_ the assumption here was the same as I had before, ie: KVM 
> arm_hcr_el2_eff() = 0?
>
> So as we changed this assumption for arm_hcr_el2_eff(), and ended up taking the 
> whole implementation for KVM too,
> we might need to do the same for fp_exception_el?

Yes, take the whole function.

The initial assumption for arm_hcr_el2_eff was correct, until nested virt came 
along.

The initial assumption for fp_exception_el was simply false.  The kernel can 
and does disable the fpu from time to time.  We were simply ignoring this for 
the purpose of arch_dump or whatever corner cases KVM actually uses this function.


r~