arch-arm: don't expose FEAT_VHE by default

If FEAT_VHE is implemented and Linux boots in EL2, it programs itself
to operate in EL2. This causes a later boot stall as explained in
https://gem5.atlassian.net/browse/GEM5-901.
We provide a parameter "have_vhe" to enable FEAT_VHE on demand. This is
disabled by default until fixed. This avoids users stalling on the common
case of booting Linux without a hypervisor.

Change-Id: I3ee7be1ca59afc0cbbda59fb3aad4c897c06405f
Signed-off-by: Adrian Herrera <adrian.herrera@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/39695
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>

src/arch/arm/ArmSystem.py

@@ -1,4 +1,4 @@
-# Copyright (c) 2009, 2012-2013, 2015-2020 ARM Limited
+# Copyright (c) 2009, 2012-2013, 2015-2021 ARM Limited
 # All rights reserved.
 #
 # The license below extends only to copyright in the software and shall
@@ -73,6 +73,8 @@ class ArmSystem(System):
         "SVE vector length in quadwords (128-bit)")
     have_lse = Param.Bool(True,
         "True if LSE is implemented (ARMv8.1)")
+    have_vhe = Param.Bool(False,
+        "True if FEAT_VHE (Virtualization Host Extensions) is implemented")
     have_pan = Param.Bool(True,
         "True if Priviledge Access Never is implemented (ARMv8.1)")
     have_secel2 = Param.Bool(True,