tcg: move qemu_tcg_configure to accel/tcg/tcg-all.c

Move everything related to mttcg_enabled in accel/tcg/tcg-all.c,
which will make even more sense when "thread" becomes a QOM property.

For now, initializing mttcg_enabled in the instance_init function
prepares for the next patch, which will only invoke qemu_tcg_configure
when the command line includes a -accel option.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 83 insertions, 0 deletions

diff --git a/accel/tcg/tcg-all.c b/accel/tcg/tcg-all.c
index c59d5b0024..6b000f0b94 100644
--- a/accel/tcg/tcg-all.c
+++ b/accel/tcg/tcg-all.c
@@ -30,6 +30,11 @@
 #include "cpu.h"
 #include "sysemu/cpus.h"
 #include "qemu/main-loop.h"
+#include "tcg/tcg.h"
+#include "include/qapi/error.h"
+#include "include/qemu/error-report.h"
+#include "include/hw/boards.h"
+#include "qemu/option.h"
 
 unsigned long tcg_tb_size;
 
@@ -58,6 +63,53 @@ static void tcg_handle_interrupt(CPUState *cpu, int mask)
     }
 }
 
+/*
+ * We default to false if we know other options have been enabled
+ * which are currently incompatible with MTTCG. Otherwise when each
+ * guest (target) has been updated to support:
+ *   - atomic instructions
+ *   - memory ordering primitives (barriers)
+ * they can set the appropriate CONFIG flags in ${target}-softmmu.mak
+ *
+ * Once a guest architecture has been converted to the new primitives
+ * there are two remaining limitations to check.
+ *
+ * - The guest can't be oversized (e.g. 64 bit guest on 32 bit host)
+ * - The host must have a stronger memory order than the guest
+ *
+ * It may be possible in future to support strong guests on weak hosts
+ * but that will require tagging all load/stores in a guest with their
+ * implicit memory order requirements which would likely slow things
+ * down a lot.
+ */
+
+static bool check_tcg_memory_orders_compatible(void)
+{
+#if defined(TCG_GUEST_DEFAULT_MO) && defined(TCG_TARGET_DEFAULT_MO)
+    return (TCG_GUEST_DEFAULT_MO & ~TCG_TARGET_DEFAULT_MO) == 0;
+#else
+    return false;
+#endif
+}
+
+static bool default_mttcg_enabled(void)
+{
+    if (use_icount || TCG_OVERSIZED_GUEST) {
+        return false;
+    } else {
+#ifdef TARGET_SUPPORTS_MTTCG
+        return check_tcg_memory_orders_compatible();
+#else
+        return false;
+#endif
+    }
+}
+
+static void tcg_accel_instance_init(Object *obj)
+{
+    mttcg_enabled = default_mttcg_enabled();
+}
+
 static int tcg_init(MachineState *ms)
 {
     tcg_exec_init(tcg_tb_size * 1024 * 1024);
@@ -65,6 +117,36 @@ static int tcg_init(MachineState *ms)
     return 0;
 }
 
+void qemu_tcg_configure(QemuOpts *opts, Error **errp)
+{
+    const char *t = qemu_opt_get(opts, "thread");
+    if (!t) {
+        return;
+    }
+    if (strcmp(t, "multi") == 0) {
+        if (TCG_OVERSIZED_GUEST) {
+            error_setg(errp, "No MTTCG when guest word size > hosts");
+        } else if (use_icount) {
+            error_setg(errp, "No MTTCG when icount is enabled");
+        } else {
+#ifndef TARGET_SUPPORTS_MTTCG
+            warn_report("Guest not yet converted to MTTCG - "
+                        "you may get unexpected results");
+#endif
+            if (!check_tcg_memory_orders_compatible()) {
+                warn_report("Guest expects a stronger memory ordering "
+                            "than the host provides");
+                error_printf("This may cause strange/hard to debug errors\n");
+            }
+            mttcg_enabled = true;
+        }
+    } else if (strcmp(t, "single") == 0) {
+        mttcg_enabled = false;
+    } else {
+        error_setg(errp, "Invalid 'thread' setting %s", t);
+    }
+}
+
 static void tcg_accel_class_init(ObjectClass *oc, void *data)
 {
     AccelClass *ac = ACCEL_CLASS(oc);
@@ -78,6 +160,7 @@ static void tcg_accel_class_init(ObjectClass *oc, void *data)
 static const TypeInfo tcg_accel_type = {
     .name = TYPE_TCG_ACCEL,
     .parent = TYPE_ACCEL,
+    .instance_init = tcg_accel_instance_init,
     .class_init = tcg_accel_class_init,
 };