diff --git a/docs/misc/arm/device-tree/booting.txt b/docs/misc/arm/device-tree/booting.txt
index f73839df09..bcb06bc796 100644
--- a/docs/misc/arm/device-tree/booting.txt
+++ b/docs/misc/arm/device-tree/booting.txt
@@ -162,6 +162,15 @@ with the following properties:
 
     An integer specifying the number of vcpus to allocate to the guest.
 
+    The resulting number of vcpus is still subject to Xen's generic and
+    architecture-specific domain limits. On Arm GICv3 systems, each vcpu
+    needs a virtual redistributor frame. Domains using the host GIC layout,
+    such as the hardware domain or direct-mapped domains, can only use vcpus
+    whose virtual redistributor frame is covered by the redistributor MMIO
+    regions exposed for that layout. If the requested number of vcpus exceeds
+    that limit, Xen will create fewer vcpus than requested, stopping at the
+    first vcpu whose virtual redistributor frame is not covered.
+
 - llc-colors
     A string specifying the LLC color configuration for the guest.
     Refer to docs/misc/cache_coloring.rst for syntax. This option is applicable
diff --git a/docs/misc/xen-command-line.pandoc b/docs/misc/xen-command-line.pandoc
index d46d5b2152..8c89b7852c 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -1000,6 +1000,9 @@ For example, with `dom0_max_vcpus=4-8`:
 >      8    |  8
 >     10    |  8
 
+The resulting number of Dom0 VCPUs is still subject to Xen's generic
+and architecture-specific domain limits.
+
 ### dom0_mem (ARM)
 > `= <size>`