arm64: Document requirement for access to FEAT_HCX

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@kernel.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20210512162350.20349-1-broonie@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>

diff --git a/Documentation/arm64/booting.rst b/Documentation/arm64/booting.rst
index 18b8cc1bf32c61433e7058ca2a11960123b412c9..a9192e7a231bf28acb8a3b4a86f316178d2196e5 100644 (file)
--- 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: