arm/arm64: KVM: vgic: Clarify and correct vgic documentation

The VGIC virtual distributor implementation documentation was written a
very long time ago, before the true nature of the beast had been
partially absorbed into my bloodstream.  Clarify the docs.

Plus, it fixes an actual bug.  ICFRn, pfff.

Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

virt/kvm/arm/vgic.c

@@ -36,21 +36,22 @@
  * How the whole thing works (courtesy of Christoffer Dall):
  *
  * - At any time, the dist->irq_pending_on_cpu is the oracle that knows if
- *   something is pending
- * - VGIC pending interrupts are stored on the vgic.irq_pending vgic
- *   bitmap (this bitmap is updated by both user land ioctls and guest
- *   mmio ops, and other in-kernel peripherals such as the
- *   arch. timers) and indicate the 'wire' state.
+ *   something is pending on the CPU interface.
+ * - Interrupts that are pending on the distributor are stored on the
+ *   vgic.irq_pending vgic bitmap (this bitmap is updated by both user land
+ *   ioctls and guest mmio ops, and other in-kernel peripherals such as the
+ *   arch. timers).
  * - Every time the bitmap changes, the irq_pending_on_cpu oracle is
  *   recalculated
  * - To calculate the oracle, we need info for each cpu from
  *   compute_pending_for_cpu, which considers:
  *   - PPI: dist->irq_pending & dist->irq_enable
  *   - SPI: dist->irq_pending & dist->irq_enable & dist->irq_spi_target
- *   - irq_spi_target is a 'formatted' version of the GICD_ICFGR
+ *   - irq_spi_target is a 'formatted' version of the GICD_ITARGETSRn
  *     registers, stored on each vcpu. We only keep one bit of
  *     information per interrupt, making sure that only one vcpu can
  *     accept the interrupt.
+ * - If any of the above state changes, we must recalculate the oracle.
  * - The same is true when injecting an interrupt, except that we only
  *   consider a single interrupt at a time. The irq_spi_cpu array
  *   contains the target CPU for each SPI.