[PATCH v2 3/9] KVM: arm64: vgic: Be tolerant to the lack of maintenance interrupt

[Marc Zyngier]

As it turns out, not all the interrupt controllers are able to
expose a vGIC maintenance interrupt as a distrete signal.
And to be fair, it doesn't really matter as all we require is
for *something* to kick us out of guest mode out way or another.

On systems that do not expose a maintenance interrupt as such,
there are two outcomes:

- either the virtual CPUIF does generate an interrupt, and
  by the time we are back to the host the interrupt will have long
  been disabled (as we set ICH_HCR_EL2.EN to 0 on exit). In this case,
  interrupt latency is as good as it gets.

- or some other event (physical timer) will take us out of the guest
  anyway, and the only drawback is a bad interrupt latency.

So let's be tolerant to the lack of maintenance interrupt, and just let
the user know that their mileage may vary...

Signed-off-by: Marc Zyngier <maz at kernel.org>
---
 arch/arm64/kvm/vgic/vgic-init.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kvm/vgic/vgic-init.c b/arch/arm64/kvm/vgic/vgic-init.c
index 9b491263f5f7..00c75495fd0c 100644
--- a/arch/arm64/kvm/vgic/vgic-init.c
+++ b/arch/arm64/kvm/vgic/vgic-init.c
@@ -521,11 +521,6 @@ int kvm_vgic_hyp_init(void)
 	if (!gic_kvm_info)
 		return -ENODEV;
 
-	if (!gic_kvm_info->maint_irq) {
-		kvm_err("No vgic maintenance irq\n");
-		return -ENXIO;
-	}
-
 	switch (gic_kvm_info->type) {
 	case GIC_V2:
 		ret = vgic_v2_probe(gic_kvm_info);
@@ -549,6 +544,11 @@ int kvm_vgic_hyp_init(void)
 	if (ret)
 		return ret;
 
+	if (!kvm_vgic_global_state.maint_irq) {
+		kvm_err("No maintenance interrupt available, fingers crossed...\n");
+		return 0;
+	}
+
 	ret = request_percpu_irq(kvm_vgic_global_state.maint_irq,
 				 vgic_maintenance_handler,
 				 "vgic", kvm_get_running_vcpus());
-- 
2.29.2