From 8cf1da729170b7cc47ebaca46912a4f37675dc95 Mon Sep 17 00:00:00 2001 From: Peter Maydell Date: Tue, 9 Jan 2024 17:08:34 +0000 Subject: [PATCH] docs/system/arm/virt.rst: Improve 'highmem' option docs MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Improve the 'highmem' option docs to note that by default we assume that a 32-bit kernel on an LPAE-capable CPU has LPAE enabled, and what the consequences are. Signed-off-by: Peter Maydell Reviewed-by: Alex Bennée Reviewed-by: Eric Auger Message-id: 20240109170834.1387457-1-peter.maydell@linaro.org --- docs/system/arm/virt.rst | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) 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.