hw/arm/virt: Enable MTE via a machine property

Control this cpu feature via a machine property, much as we do
with secure=on, since both require specialized support in the
machine setup to be functional.

Default MTE to off, since this feature implies extra overhead.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20200713213341.590275-2-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

2 files changed, 14 insertions, 10 deletions

diff --git a/target/arm/cpu.c b/target/arm/cpu.c
index 5050e1843a..111579554f 100644
--- a/target/arm/cpu.c
+++ b/target/arm/cpu.c
@@ -1698,6 +1698,17 @@ static void arm_cpu_realizefn(DeviceState *dev, Error **errp)
         cpu->id_pfr1 &= ~0xf000;
     }
 
+#ifndef CONFIG_USER_ONLY
+    if (cpu->tag_memory == NULL && cpu_isar_feature(aa64_mte, cpu)) {
+        /*
+         * Disable the MTE feature bits if we do not have tag-memory
+         * provided by the machine.
+         */
+        cpu->isar.id_aa64pfr1 =
+            FIELD_DP64(cpu->isar.id_aa64pfr1, ID_AA64PFR1, MTE, 0);
+    }
+#endif
+
     /* MPU can be configured out of a PMSA CPU either by setting has-mpu
      * to false or by setting pmsav7-dregion to 0.
      */
@@ -1787,14 +1798,6 @@ static void arm_cpu_realizefn(DeviceState *dev, Error **errp)
             cpu_address_space_init(cs, ARMASIdx_TagS, "cpu-tag-memory",
                                    cpu->secure_tag_memory);
         }
-    } else if (cpu_isar_feature(aa64_mte, cpu)) {
-        /*
-         * Since there is no tag memory, we can't meaningfully support MTE
-         * to its fullest.  To avoid problems later, when we would come to
-         * use the tag memory, downgrade support to insns only.
-         */
-        cpu->isar.id_aa64pfr1 =
-            FIELD_DP64(cpu->isar.id_aa64pfr1, ID_AA64PFR1, MTE, 1);
     }
 
     cpu_address_space_init(cs, ARMASIdx_NS, "cpu-memory", cs->memory);
diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c
index 15494002d2..dd696183df 100644
--- a/target/arm/cpu64.c
+++ b/target/arm/cpu64.c
@@ -646,8 +646,9 @@ static void aarch64_max_initfn(Object *obj)
         t = cpu->isar.id_aa64pfr1;
         t = FIELD_DP64(t, ID_AA64PFR1, BT, 1);
         /*
-         * Begin with full support for MTE; will be downgraded to MTE=1
-         * during realize if the board provides no tag memory.
+         * Begin with full support for MTE. This will be downgraded to MTE=0
+         * during realize if the board provides no tag memory, much like
+         * we do for EL2 with the virtualization=on property.
          */
         t = FIELD_DP64(t, ID_AA64PFR1, MTE, 2);
         cpu->isar.id_aa64pfr1 = t;