Added Ssstrict option.

rva23-profile.adoc

@@ -320,8 +320,8 @@ NOTE: The following extensions were required when the hypervisor was implemented
 ==== RVA23S64 Optional Extensions
 
 RVA23S64 has ten unprivileged options (Zvkng, Zvksg, Zacas, Zvbc, Zfh,
-Zbc, Zvfh, Zfbfmin, Zvfbfmin, Zvfbfwma) from RVA23U64, and five
-privileged options (Sv48, Sv57, Svadu, Zkr, Sdext).
+Zbc, Zvfh, Zfbfmin, Zvfbfmin, Zvfbfwma) from RVA23U64, and six
+privileged options (Sv48, Sv57, Svadu, Zkr, Sdext, Ssstrict).
 
 ===== Localized Options
 
@@ -347,14 +347,24 @@ The following are new privileged expansion options in RVA23S64
 
 - *Sdext* Debug triggers
 
+- *Ssstrict* No non-conforming extensions are present.  Attempts to
+   execute unimplemented opcodes or access unimplemented CSRs in the
+   standard or reserved encoding spaces raises an illegal instruction
+   exception that results in a contained trap to the supervisor-mode
+   trap handler.
+
+NOTE: Ssstrict does not prescribe behavior for the custom encoding
+spaces or CSRs.
+
 ===== Transitory Options
 
 There are no privileged transitory options in RVA23S64.
 
 ==== RVA23S64 Recommendations
 
-- Implementations are strongly recommended to raise illegal-instruction
-  exceptions when attempting to execute unimplemented opcodes.
+- Implementations are strongly recommended to raise
+  illegal-instruction exceptions when attempting to execute
+  unimplemented opcodes or access unimplemented CSRs.
 
 == Glossary of ISA Extensions