Re: [PATCH 18/28] KVM: arm64: Add kvm_has_nv{2,3}() predicates

[Marc Zyngier <maz@kernel.org>]

On Thu, 02 Jul 2026 17:25:17 +0100,
sashiko-bot@kernel.org wrote:
> 
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] `is_nested_nv3_ctxt()` incorrectly identifies NV3 context when the guest clears `HCR_EL2.E2H`, diverging from hardware execution semantics.
> --
> 
> commit c75857355bb73ff60c1d0206705bb863784f8183
> Author: Marc Zyngier <maz@kernel.org>
> 
> KVM: arm64: Add kvm_has_nv{2,3}() predicates
> 
> Add a new set of predicates indicating whether VM is capable of
> NV2, NV3, and is in a nested NV3 context. This is going to become
> useful as we start dealing with a mix of behaviours.
> 
> > diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> > index 9831166695186..c562d8171d5e1 100644
> > --- a/arch/arm64/include/asm/kvm_emulate.h
> > +++ b/arch/arm64/include/asm/kvm_emulate.h
> 
> [ ... ]
> 
> > +static inline bool kvm_has_nv3(struct kvm *kvm)
> > +{
> > +	return (cpus_have_final_cap(ARM64_HAS_NESTED_VIRT) &&
> > +		cpus_have_final_cap(ARM64_HAS_NV3) &&
> > +		kvm_has_feat(kvm, ID_AA64MMFR4_EL1, NV_frac, NV3));
> > +}
> > +
> > +static inline bool is_nested_nv3_ctxt(struct kvm_vcpu *vcpu)
> > +{
> > +	return (has_vhe() && kvm_has_nv3(vcpu->kvm) && is_nested_ctxt(vcpu) &&
> > +		(__vcpu_sys_reg(vcpu, HCR_EL2) & HCR_EL2_NV) &&
> > +		(__vcpu_sys_reg(vcpu, HCRX_EL2) & HCRX_EL2_NVTGE));
> > +}
> 
> [Severity: High]
> Does this predicate miss a mandatory check for HCR_EL2.E2H?
> 
> Architecturally, NVTGE is RES0 when E2H is 0. If a guest sets HCR_EL2.NV = 1
> and HCRX_EL2.NVTGE = 1, but leaves HCR_EL2.E2H = 0, the hardware will not
> execute the guest under NV3 semantics.

Stop inventing the architecture. NV3 is only applicable to E2H==1, and
KVM doesn't allow NV with E2H==0.

	M.

-- 
Jazz isn't dead. It just smells funny.