[PATCH] arm64: Document requirement for access to FEAT_HCX

[Mark Brown]

v8.7 of the architecture introduced FEAT_HCX which adds an additional
hypervisor configuration register HCRX_EL2. Even though Linux does not
currently make use of this feature let's document that the EL3 trap for
access to the register should be disabled so that we are able to make
use of it in future.

Signed-off-by: Mark Brown <broonie at kernel.org>
---
 Documentation/arm64/booting.rst | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/arm64/booting.rst b/Documentation/arm64/booting.rst
index 18b8cc1bf32c..a9192e7a231b 100644
--- a/Documentation/arm64/booting.rst
+++ b/Documentation/arm64/booting.rst
@@ -277,6 +277,12 @@ Before jumping into the kernel, the following conditions must be met:
 
     - SCR_EL3.FGTEn (bit 27) must be initialised to 0b1.
 
+  For CPUs with support for HCRX_EL2 (FEAT_HCX) present:
+
+  - If EL3 is present and the kernel is entered at EL2:
+
+    - SCR_EL3.HXEn (bit 38) must be initialised to 0b1.
+
   For CPUs with Advanced SIMD and floating point support:
 
   - If EL3 is present:
-- 
2.20.1