[PATCH v2 4/5] KVM: arm64: vgic: Do not access the GICv5 CPU interface from EL1

[Fuad Tabba <fuad.tabba@linux.dev>]

can_access_vgic_from_kernel() excludes only the GICv3 system register
interface, so on a native GICv5 system without FEAT_GCIE_LEGACY it
returns true under nVHE. The kernel then saves and restores the CPU
interface from EL1, where ICH_VMCR_EL2 and the ICH_PPI_* registers are
UNDEFINED, so running a vCPU oopses the host. The nVHE world switch
already does that work at EL2.

Require VHE for GICv5 as for GICv3.

Fixes: 9b8e3d4ca0e73 ("KVM: arm64: gic-v5: Implement GICv5 load/put and save/restore")
Reviewed-by: Sascha Bischoff <sascha.bischoff@arm.com>
Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
---
 arch/arm64/kvm/vgic/vgic.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kvm/vgic/vgic.c b/arch/arm64/kvm/vgic/vgic.c
index b25303d9919fd..da72779d3b3ee 100644
--- a/arch/arm64/kvm/vgic/vgic.c
+++ b/arch/arm64/kvm/vgic/vgic.c
@@ -1045,11 +1045,15 @@ static void vgic_flush_lr_state(struct kvm_vcpu *vcpu)
 static inline bool can_access_vgic_from_kernel(void)
 {
 	/*
-	 * GICv2 can always be accessed from the kernel because it is
-	 * memory-mapped, and VHE systems can access GICv3 EL2 system
-	 * registers.
+	 * GICv3 and GICv5 drive the CPU interface through EL2 system
+	 * registers, so only VHE reaches them from the kernel. GICv2 is
+	 * memory-mapped and always reachable.
 	 */
-	return !static_branch_unlikely(&kvm_vgic_global_state.gicv3_cpuif) || has_vhe();
+	if (static_branch_unlikely(&kvm_vgic_global_state.gicv3_cpuif) ||
+	    kvm_vgic_global_state.type == VGIC_V5)
+		return has_vhe();
+
+	return true;
 }
 
 static inline void vgic_save_state(struct kvm_vcpu *vcpu)
-- 
2.39.5