lib: el3_runtime: Conditionally save/restore EL2 NEVE registers

Include EL2 registers related to Nested Virtualization in EL2 context
save/restore routines if architecture supports it and platform wants to
use these features in Secure world.

Change-Id: If006ab83bbc2576488686f5ffdff88b91adced5c
Signed-off-by: Arunachalam Ganapathy <arunachalam.ganapathy@arm.com>

Makefile

@@ -865,6 +865,7 @@ $(eval $(call assert_booleans,\
         CTX_INCLUDE_PAUTH_REGS \
         CTX_INCLUDE_MTE_REGS \
         CTX_INCLUDE_EL2_REGS \
+        CTX_INCLUDE_NEVE_REGS \
         DEBUG \
         DYN_DISABLE_AUTH \
         EL3_EXCEPTION_HANDLING \
@@ -953,6 +954,7 @@ $(eval $(call add_defines,\
         EL3_EXCEPTION_HANDLING \
         CTX_INCLUDE_MTE_REGS \
         CTX_INCLUDE_EL2_REGS \
+        CTX_INCLUDE_NEVE_REGS \
         DECRYPTION_SUPPORT_${DECRYPTION_SUPPORT} \
         ENABLE_AMU \
         ENABLE_ASSERTIONS \

docs/getting_started/build-options.rst

@@ -161,6 +161,10 @@ Common build options
    registers to be included when saving and restoring the CPU context. Default
    is 0.
 
+-  ``CTX_INCLUDE_NEVE_REGS``: Boolean option that, when set to 1, will cause the
+   Armv8.4-NV registers to be saved/restored when entering/exiting an EL2
+   execution context. Default value is 0.
+
 -  ``CTX_INCLUDE_PAUTH_REGS``: Boolean option that, when set to 1, enables
    Pointer Authentication for Secure world. This will cause the ARMv8.3-PAuth
    registers to be included when saving and restoring the CPU context as

lib/el3_runtime/aarch64/context.S

@@ -200,8 +200,10 @@ func el2_sysregs_context_save
 	mrs	x12, vdisr_el2
 	str	x12, [x0, #CTX_VDISR_EL2]
 
+#if CTX_INCLUDE_NEVE_REGS
 	mrs	x13, vncr_el2
 	str	x13, [x0, #CTX_VNCR_EL2]
+#endif
 
 	mrs	x14, vsesr_el2
 	str	x14, [x0, #CTX_VSESR_EL2]
@@ -395,8 +397,10 @@ func el2_sysregs_context_restore
 	ldr	x13, [x0, #CTX_VDISR_EL2]
 	msr	vdisr_el2, x13
 
+#if CTX_INCLUDE_NEVE_REGS
 	ldr	x14, [x0, #CTX_VNCR_EL2]
 	msr	vncr_el2, x14
+#endif
 
 	ldr	x15, [x0, #CTX_VSESR_EL2]
 	msr	vsesr_el2, x15

make_helpers/defaults.mk

@@ -62,6 +62,11 @@ CTX_INCLUDE_FPREGS		:= 0
 # world. It is not needed to use it in the Non-secure world.
 CTX_INCLUDE_PAUTH_REGS		:= 0
 
+# Include Nested virtualization control (Armv8.4-NV) registers in cpu context.
+# This must be set to 1 if architecture implements Nested Virtualization
+# Extension and platform wants to use this feature in the Secure world
+CTX_INCLUDE_NEVE_REGS		:= 0
+
 # Debug build
 DEBUG				:= 0