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

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

[Marc Zyngier]

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

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

[Mark Brown]

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On Fri, Nov 14, 2025 at 09:35:41AM +0000, Marc Zyngier 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.

This resolves the issues I was seeing with no-vgic-v3:

Tested-by: Mark Brown <broonie@kernel.org>

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