docs/arm: Document where Xen should be loaded in memory

In commit 9d267c049d92 ("xen/arm64: Rework the memory layout"),
we decided to require Xen to be loaded below 2 TiB to simplify
the logic to enable the MMU. The limit was decided based on
how known platform boot plus some slack.

We had a recent report that this is not sufficient on the AVA
platform with a old firmware [1]. But the restriction is not
going to change in Xen 4.18. So document the limit clearly
in docs/misc/arm/booting.txt.

[1] https://lore.kernel.org/20231013122658.1270506-3-leo.yan@linaro.org

Signed-off-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Michal Orzel <michal.orzel@amd.com>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>
Release-acked-by: Henry Wang <Henry.Wang@arm.com>

diff --git a/docs/misc/arm/booting.txt b/docs/misc/arm/booting.txt
index 02f7bb65ec6d99e0f2f72e769847406610ec4873..547f58a7d98194e179afdeaa4e2284bba1cd268f 100644 (file)
--- a/docs/misc/arm/booting.txt
+++ b/docs/misc/arm/booting.txt
@@ -21,7 +21,9 @@ The exceptions to this on 32-bit ARM are as follows:
  zImage protocol should still be used and not the stricter "raw
  (non-zImage)" protocol described in arm/Booting.
 
-There are no exception on 64-bit ARM.
+The exceptions to this on 64-bit ARM are as follows:
+
+ Xen binary should be loaded in memory below 2 TiB.
 
 Booting Guests
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