Docs: Update out-of-date description for RoT Services
FF-M updates the description about whether an RoT Service is a
Secure Partition RoT service. Update the implementation document
to address the change.
Signed-off-by: Ken Liu <Ken.Liu@arm.com>
Change-Id: Ia150f8ffdfbd77d90a8b0b13193dc7df6ba434be
diff --git a/docs/technical_references/design_docs/ff_isolation.rst b/docs/technical_references/design_docs/ff_isolation.rst
index e1bbaca..dd3140d 100644
--- a/docs/technical_references/design_docs/ff_isolation.rst
+++ b/docs/technical_references/design_docs/ff_isolation.rst
@@ -43,14 +43,19 @@
Partitions.
.. important::
- The PSA RoT Services can be implemented directly within the SPM, or as RoT
- Services within one or more PSA RoT Secure Partitions. But if the PSA RoT
- Services needs to be accessed by NSPE or Application RoT of Trust Services
- must be implemented in a Secure Partitions (Please refer to chapter 2.4 -
- "RoT Services" of `Firmware Framework for M (FF-M)`_).
- The implementation in this design treats the PSA RoT Secure Partition in the
- PSA RoT domain to follow `L3.3` above and relax `L3.2` for PSA RoT Secure
- Partition under isolation level 3.
+ A Secure Partition RoT Service is a Root of Trust Service implemented within
+ a Secure Partition. An Application RoT Service must be implemented as
+ a Secure Partition RoT Service. But it is implementation-defined whether a
+ PSA RoT Service is a Secure Partition RoT Service.
+
+ Here listed several possible PSA RoT Service implementation mechanisms:
+
+ 1. Implement them in Secure Partitions with respective boundaries.
+ 2. Implement them in Secure Partitions, but no boundaries between these
+ Secure Partitions.
+ 3. Implement them in a customized way instead of Secure Partitions.
+
+ TF-M chooses the 2nd option to balance performance and complexity.
Isolation Rules
===============