[RFC PATCH 06/13] KVM: arm64: Resolve race between vCPU scheduling and vLPI enablement

[Maximilian Dittgen]

If vgic_v4_load() is called to schedule GICv4 on a vCPU at the same
time that kvm_vgic_enable_vcpu_vlpi() is called to enable vLPI
direct injection on the vCPU, vgic_v4_load() will attempt to
map the vCPU's doorbell IRQ to the physical processor while
kvm_vgic_enable_vcpu_vlpi() is still creating the doorbell IRQ.

This race will cause vgic_v4_load()'s mapping operation to fail,
triggering a WARN_ON in vgic_v3_load().

Fix by checking for the presence of a doorbell IRQ before attempting
to load GICv4. Remove WARN_ON to remove verbosity of GICv4 load
failures resulting from this race; failure to load GICv4 is not
breaking behavior.

Signed-off-by: Maximilian Dittgen <mdittgen at amazon.com>
---
 arch/arm64/kvm/vgic/vgic-v3.c | 2 +-
 arch/arm64/kvm/vgic/vgic-v4.c | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/vgic/vgic-v3.c b/arch/arm64/kvm/vgic/vgic-v3.c
index 842a3a50f3a2..ffaf692399fd 100644
--- a/arch/arm64/kvm/vgic/vgic-v3.c
+++ b/arch/arm64/kvm/vgic/vgic-v3.c
@@ -995,7 +995,7 @@ void vgic_v3_load(struct kvm_vcpu *vcpu)
 	if (has_vhe())
 		__vgic_v3_activate_traps(cpu_if);
 
-	WARN_ON(vgic_v4_load(vcpu));
+	vgic_v4_load(vcpu);
 }
 
 void vgic_v3_put(struct kvm_vcpu *vcpu)
diff --git a/arch/arm64/kvm/vgic/vgic-v4.c b/arch/arm64/kvm/vgic/vgic-v4.c
index efb9ac9188e3..0affcfca17f0 100644
--- a/arch/arm64/kvm/vgic/vgic-v4.c
+++ b/arch/arm64/kvm/vgic/vgic-v4.c
@@ -454,6 +454,7 @@ int vgic_v4_load(struct kvm_vcpu *vcpu)
 
 	if (!vgic_supports_direct_irqs(vcpu->kvm) ||
 				!vpe->its_vm ||
+				!vpe->irq || /* check if irq has been allocated yet */
 				vpe->resident)
 		return 0;
 
-- 
2.50.1 (Apple Git-155)




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