[PATCH v9 20/26] target/arm/kvm: Ignore and trace unexpected writable reserved fields

[Eric Auger <eric.auger@redhat.com>]

KVM currently reports some bits as writable whereas they are
RES0 or RAZ. The code easily allows to do some sanity checking
for such inconsistencies. Let's add a trace event when this is
encountered and skip the field

Signed-off-by: Eric Auger <eric.auger@redhat.com>

---
v8 -> v9
- fix bug reported by Shameer (map &= ~MAKE_64BIT_MASK(lower,
  field->length);)
---
 target/arm/kvm.c        | 10 ++++++++++
 target/arm/trace-events |  1 +
 2 files changed, 11 insertions(+)

diff --git a/target/arm/kvm.c b/target/arm/kvm.c
index f52c03745e..537673177a 100644
--- a/target/arm/kvm.c
+++ b/target/arm/kvm.c
@@ -548,6 +548,16 @@ decode_idreg_writemap(Object *obj, ARM64SysReg *reg)
         }
         lower = field->shift;
         upper = field->shift + field->length - 1;
+
+        /* Sanity check the field is not a reserved field */
+        if (strstr(field->name, "RES0") || strstr(field->name, "RES1") ||
+            strstr(field->name, "RAZ")) {
+            trace_unexpected_writable_reserved_field(reg->name, field->name,
+                                                     lower, upper);
+            map &= ~MAKE_64BIT_MASK(lower, field->length);
+            i = ctz64(map);
+            continue;
+        }
         prop_name = g_strdup_printf("SYSREG_%s_%s", reg->name, field->name);
         trace_decode_idreg_writemap(field->name, lower, upper, prop_name);
         object_property_add(obj, prop_name, "uint64",
diff --git a/target/arm/trace-events b/target/arm/trace-events
index b4d2b45a7d..2a9cc67035 100644
--- a/target/arm/trace-events
+++ b/target/arm/trace-events
@@ -20,6 +20,7 @@ get_sysreg_prop(const char *name, uint64_t value) "%s 0x%"PRIx64
 set_sysreg_prop(const char *name, uint64_t old, uint64_t mask, uint64_t field_value, uint64_t new) "%s old reg value=0x%"PRIx64" mask=0x%"PRIx64" new field value=0x%"PRIx64" new reg value=0x%"PRIx64
 apply_sysreg_prop(const char *reg_name, const char *field_name, uint64_t old, uint64_t current, uint64_t mask, uint64_t field_value, uint64_t new) "%s.%s old=0x%"PRIx64" current=0x%"PRIx64" mask=0x%"PRIx64" new field value=0x%"PRIx64" new=0x%"PRIx64
 nb_sysreg_props(const char *name, int count) "%s: %d SYSREG properties"
+unexpected_writable_reserved_field(const char *reg_name, const char *field_name, int lower, int upper) "Unexpected writable reserved field: %s.%s [%d,%d], skip it ..."
 
 # cpu.c
 arm_cpu_reset(uint64_t mp_aff) "cpu %" PRIu64
-- 
2.53.0