KVM: arm64: WARN if unmapping a vLPI fails in any path

When unmapping a vLPI, WARN if nullifying vCPU affinity fails, not just if
failure occurs when freeing an ITE.  If undoing vCPU affinity fails, then
odds are very good that vLPI state tracking has has gotten out of whack,
i.e. that KVM and the GIC disagree on the state of an IRQ/vLPI.  At best,
inconsistent state means there is a lurking bug/flaw somewhere.  At worst,
the inconsistency could eventually be fatal to the host, e.g. if an ITS
command fails because KVM's view of things doesn't match reality/hardware.

Note, only the call from kvm_arch_irq_bypass_del_producer() by way of
kvm_vgic_v4_unset_forwarding() doesn't already WARN.  Common KVM's
kvm_irq_routing_update() WARNs if kvm_arch_update_irqfd_routing() fails.
For that path, if its_unmap_vlpi() fails in kvm_vgic_v4_unset_forwarding(),
the only possible causes are that the GIC doesn't have a v4 ITS (from
its_irq_set_vcpu_affinity()):

        /* Need a v4 ITS */
        if (!is_v4(its_dev->its))
                return -EINVAL;

        guard(raw_spinlock)(&its_dev->event_map.vlpi_lock);

        /* Unmap request? */
        if (!info)
                return its_vlpi_unmap(d);

or that KVM has gotten out of sync with the GIC/ITS (from its_vlpi_unmap()):

        if (!its_dev->event_map.vm || !irqd_is_forwarded_to_vcpu(d))
                return -EINVAL;

All of the above failure scenarios are warnable offences, as they should
never occur absent a kernel/KVM bug.

Acked-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/all/aFWY2LTVIxz5rfhh@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/irqchip/irq-gic-v4.c b/drivers/irqchip/irq-gic-v4.c
index 58c28895f8c4..8455b4a5fbb0 100644
--- a/drivers/irqchip/irq-gic-v4.c
+++ b/drivers/irqchip/irq-gic-v4.c
@@ -342,10 +342,10 @@ int its_get_vlpi(int irq, struct its_vlpi_map *map)
 	return irq_set_vcpu_affinity(irq, &info);
 }
 
-int its_unmap_vlpi(int irq)
+void its_unmap_vlpi(int irq)
 {
 	irq_clear_status_flags(irq, IRQ_DISABLE_UNLAZY);
-	return irq_set_vcpu_affinity(irq, NULL);
+	WARN_ON_ONCE(irq_set_vcpu_affinity(irq, NULL));
 }
 
 int its_prop_update_vlpi(int irq, u8 config, bool inv)