xen: arm: Document xenheap_megabytes limitation

In setup_mm(), the value passed as xenheap_megabytes gets
converted to pages and passed to setup_xenheap_mappings(),
which in turn passes it to create_32mb_mappings(), which
contains an ASSERT that the value passed is a multiple of
32MB. So specifying any value that is not an integer multiple
of 32 will cause Xen to hit this assert and fail to boot.

Signed-off-by: Chris Brand <chris.brand@broadcom.com>
Reviewed-by: Julien Grall <julien.grall@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

diff --git a/docs/misc/xen-command-line.markdown b/docs/misc/xen-command-line.markdown
index 70d7ab8234bc8cdeae6045ccb093b9485933fac5..a1bca2b35fbc3ebbda280c39f41b8714f26b03f5 100644 (file)
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -242,7 +242,7 @@ the NMI watchdog is also enabled.
 
 > Default: `0` (1/32 of RAM)
 
-Amount of RAM to set aside for the Xenheap.
+Amount of RAM to set aside for the Xenheap. Must be an integer multiple of 32.
 
 By default will use 1/32 of the RAM up to a maximum of 1GB and with a
 minimum of 32M, subject to a suitably aligned and sized contiguous