KVM: arm64: Add undocumented return values for PMU device control group

KVM_ARM_VCPU_PMU_V3_IRQ returns -EFAULT if get_user() fails when reading
the interrupt number from kvm_device_attr.addr.

KVM_ARM_VCPU_PMU_V3_INIT returns the error value from kvm_vgic_set_owner().
kvm_arm_pmu_v3_init() checks that the vgic has been initialized and the
interrupt number is valid, but kvm_vgic_set_owner() can still return the
error code -EEXIST if another device has already claimed the interrupt.
Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Link: https://lore.kernel.org/r/20200924123731.268177-2-alexandru.elisei@arm.com

Documentation/virt/kvm/devices/vcpu.rst

@@ -25,6 +25,7 @@ Returns:
 
 	 =======  ========================================================
 	 -EBUSY   The PMU overflow interrupt is already set
+	 -EFAULT  Error reading interrupt number
 	 -ENXIO   The overflow interrupt not set when attempting to get it
 	 -ENODEV  PMUv3 not supported
 	 -EINVAL  Invalid PMU overflow interrupt number supplied or
@@ -45,6 +46,7 @@ all vcpus, while as an SPI it must be a separate number per vcpu.
 Returns:
 
 	 =======  ======================================================
+	 -EEXIST  Interrupt number already used
 	 -ENODEV  PMUv3 not supported or GIC not initialized
 	 -ENXIO   PMUv3 not properly configured or in-kernel irqchip not
 		  configured as required prior to calling this attribute