[PATCH v3 1/5] KVM: arm64: GICv3: Don't advertise ICH_HCR_EL2.En==1 when no vgic is configured

[Fuad Tabba]

Hi Marc,

On Mon, 17 Nov 2025 at 09:15, Marc Zyngier <maz at kernel.org> wrote:
>
> Configuring GICv3 to deal with the lack of GIC in the guest relies
> on not setting ICH_HCR_EL2.En in the shadow register, as this is
> an indication of the fact that we want to trap all system registers
> to report an UNDEF in the guest.
>
> Make sure we leave vgic_hcr untouched in this case.
>
> Reported-by: Mark Brown <broonie at kernel.org>
> Tested-by: Mark Brown <broonie at kernel.org>
> Closes: https://lore.kernel.org/r/72e1e8b5-e397-4dc5-9cd6-a32b6af3d739@sirena.org.uk
> Fixes: 877324a1b5415 ("KVM: arm64: Revamp vgic maintenance interrupt configuration")
> Signed-off-by: Marc Zyngier <maz at kernel.org>
> ---
>  arch/arm64/kvm/vgic/vgic-v3.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/arch/arm64/kvm/vgic/vgic-v3.c b/arch/arm64/kvm/vgic/vgic-v3.c
> index 598621b14a30d..1d6dd1b545bdd 100644
> --- a/arch/arm64/kvm/vgic/vgic-v3.c
> +++ b/arch/arm64/kvm/vgic/vgic-v3.c
> @@ -26,6 +26,9 @@ void vgic_v3_configure_hcr(struct kvm_vcpu *vcpu,
>  {
>         struct vgic_v3_cpu_if *cpuif = &vcpu->arch.vgic_cpu.vgic_v3;
>
> +       if (!irqchip_in_kernel(vcpu->kvm))
> +               return;
> +

Bear with me, since I'm not too familiar with this code. This is the
only function that initializes cpuif->vgic_hcr. Should we be
explicitly setting it to 0, or warn if ICH_HCR_EL2_En is set?

Cheers,
/fuad

>         cpuif->vgic_hcr = ICH_HCR_EL2_En;
>
>         if (irqs_pending_outside_lrs(als))
> --
> 2.47.3
>
>