[PATCH v4 02/36] arm64: Document boot requirements for Guarded Control Stacks

[Mark Brown]

FEAT_GCS introduces a number of new system registers, we require that
access to these registers is not trapped when we identify that the feature
is detected.

Signed-off-by: Mark Brown <broonie at kernel.org>
---
 Documentation/arch/arm64/booting.rst | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/Documentation/arch/arm64/booting.rst b/Documentation/arch/arm64/booting.rst
index b57776a68f15..de3679770c64 100644
--- a/Documentation/arch/arm64/booting.rst
+++ b/Documentation/arch/arm64/booting.rst
@@ -411,6 +411,28 @@ Before jumping into the kernel, the following conditions must be met:
 
     - HFGRWR_EL2.nPIRE0_EL1 (bit 57) must be initialised to 0b1.
 
+ - For features with Guarded Control Stacks (FEAT_GCS):
+
+  - If EL3 is present:
+
+    - SCR_EL3.GCSEn (bit 39) must be initialised to 0b1.
+
+ - If the kernel is entered at EL1 and EL2 is present:
+
+    - HFGITR_EL2.nGCSEPP (bit 59) must be initialised to 0b1.
+
+    - HFGITR_EL2.nGCSSTR_EL1 (bit 58) must be initialised to 0b1.
+
+    - HFGITR_EL2.nGCSPUSHM_EL1 (bit 57) must be initialised to 0b1.
+
+    - HFGRTR_EL2.nGCS_EL1 (bit 53) must be initialised to 0b1.
+
+    - HFGRTR_EL2.nGCS_EL0 (bit 52) must be initialised to 0b1.
+
+    - HFGWTR_EL2.nGCS_EL1 (bit 53) must be initialised to 0b1.
+
+    - HFGWTR_EL2.nGCS_EL0 (bit 52) must be initialised to 0b1.
+
 The requirements described above for CPU mode, caches, MMUs, architected
 timers, coherency and system registers apply to all CPUs.  All CPUs must
 enter the kernel in the same exception level.  Where the values documented

-- 
2.30.2