KVM: arm64: vgic-v3: Fix some error codes when setting RDIST base

KVM_DEV_ARM_VGIC_GRP_ADDR group doc says we should return
-EEXIST in case the base address of the redist is already set.
We currently return -EINVAL.

However we need to return -EINVAL in case a legacy REDIST address
is attempted to be set while REDIST_REGIONS were set. This case
is discriminated by looking at the count field.
Signed-off-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210405163941.510258-2-eric.auger@redhat.com

arch/arm64/kvm/vgic/vgic-mmio-v3.c

@@ -791,10 +791,6 @@ static int vgic_v3_insert_redist_region(struct kvm *kvm, uint32_t index,
 	size_t size = count * KVM_VGIC_V3_REDIST_SIZE;
 	int ret;
 
-	/* single rdist region already set ?*/
-	if (!count && !list_empty(rd_regions))
-		return -EINVAL;
-
 	/* cross the end of memory ? */
 	if (base + size < base)
 		return -EINVAL;
@@ -805,11 +801,15 @@ static int vgic_v3_insert_redist_region(struct kvm *kvm, uint32_t index,
 	} else {
 		rdreg = list_last_entry(rd_regions,
 					struct vgic_redist_region, list);
-		if (index != rdreg->index + 1)
+
+		/* Don't mix single region and discrete redist regions */
+		if (!count && rdreg->count)
 			return -EINVAL;
 
-		/* Cannot add an explicitly sized regions after legacy region */
-		if (!rdreg->count)
+		if (!count)
+			return -EEXIST;
+
+		if (index != rdreg->index + 1)
 			return -EINVAL;
 	}