[RFC PATCH] target/arm: disable FEAT_SME if we turn off SVE

["Alex Bennée" <alex.bennee@linaro.org>]

Before this change booting a -cpu max,sve=off would trigger and
assert:

  qemu-system-aarch64: ../../target/arm/helper.c:6647: sve_vqm1_for_el_sm: Assertion `sm' failed.

when the guest attempts to write to SMCR which shouldn't even exist if
SVE has been turned off.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
---
 target/arm/cpu64.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c
index 0e021960fb..a38d43421a 100644
--- a/target/arm/cpu64.c
+++ b/target/arm/cpu64.c
@@ -409,6 +409,13 @@ static void cpu_arm_set_sve(Object *obj, bool value, Error **errp)
     t = cpu->isar.id_aa64pfr0;
     t = FIELD_DP64(t, ID_AA64PFR0, SVE, value);
     cpu->isar.id_aa64pfr0 = t;
+
+    /* FEAT_SME requires SVE, so disable it if no SVE */
+    if (!value) {
+        t = cpu->isar.id_aa64pfr1;
+        t = FIELD_DP64(t, ID_AA64PFR1, SME, 0);
+        cpu->isar.id_aa64pfr1 = t;
+    }
 }
 
 void arm_cpu_sme_finalize(ARMCPU *cpu, Error **errp)
-- 
2.39.1