Re: [PATCH 1/4] KVM: arm64: nv: Respect exception routing rules for SEAs

[Oliver Upton <oliver.upton@linux.dev>]

Hey,

On Sat, May 31, 2025 at 05:23:44PM +0100, Marc Zyngier wrote:
> > +int kvm_inject_nested_sea(struct kvm_vcpu *vcpu, bool iabt, u64 addr)
> > +{
> > +	u64 esr;
> > +
> > +	/*
> > +	 * The destination EL is in the same translation regime as the origin;
> > +	 * directly inject the SEA.
> > +	 */
> > +	if (is_hyp_ctxt(vcpu) || !(__vcpu_sys_reg(vcpu, HCR_EL2) & HCR_TEA)) {
> > +		__kvm_inject_sea(vcpu, iabt, addr);
> > +		return 1;
> > +	}
> 
> I find this a bit confusing.
> 
> Here, we end-up *not* injecting a nested exception, but instead
> delivering it in context. I think it would be clearer to move this
> condition in kvm_inject_sea(), and then make __kvm_inject_sea()
> static.

So I went about it this way because I didn't like having NV-specific
triage outside of the nested code, though I agree the meaning of this
helper is a bit muddied. The routing is simple now but...

> Other than my rambling above, this looks rather good. But there is a
> bit more, "thanks" to FEAT_DoubleFault2:
> 
> - HCRX_EL2.TMEA also affects this patch, both on the SEA and SError
>   paths (both can be routed to EL2 when masked).
> 
> - SCTLR2_EL{1,2}2.EASE also influence the delivery of the SEA,
>   upgrading it to a SError (yes, this is the routing from hell and
>   ties directly into the following patches).

This is gonna be an ugly pile to deal with later on. Anyway, I'll pull
apart the routing / emulated exception entry to keep in-context
injection out of NV coed.

> I was expecting to see FEAT_RAS being enabled at some point, but
> that's not the case yet. Are you planning to do so?

Yup, still planning on it. Just wanted to flush out bug fixes on list.

Thanks,
Oliver