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-rw-r--r--docs/system/arm/virt.rst8
1 files changed, 7 insertions, 1 deletions
diff --git a/docs/system/arm/virt.rst b/docs/system/arm/virt.rst
index 7c4c80180c..c245c52b7a 100644
--- a/docs/system/arm/virt.rst
+++ b/docs/system/arm/virt.rst
@@ -96,7 +96,13 @@ mte
highmem
Set ``on``/``off`` to enable/disable placing devices and RAM in physical
address space above 32 bits. The default is ``on`` for machine types
- later than ``virt-2.12``.
+ later than ``virt-2.12`` when the CPU supports an address space
+ bigger than 32 bits (i.e. 64-bit CPUs, and 32-bit CPUs with the
+ Large Physical Address Extension (LPAE) feature). If you want to
+ boot a 32-bit kernel which does not have ``CONFIG_LPAE`` enabled on
+ a CPU type which implements LPAE, you will need to manually set
+ this to ``off``; otherwise some devices, such as the PCI controller,
+ will not be accessible.
compact-highmem
Set ``on``/``off`` to enable/disable the compact layout for high memory regions.