1 files changed, 164 insertions, 0 deletions
diff --git a/contrib/plugins/ips.c b/contrib/plugins/ips.c
new file mode 100644
index 0000000..29fa556
--- /dev/null
+++ b/contrib/plugins/ips.c
@@ -0,0 +1,164 @@
+/*
+ * Instructions Per Second (IPS) rate limiting plugin.
+ *
+ * This plugin can be used to restrict the execution of a system to a
+ * particular number of Instructions Per Second (IPS). This controls
+ * time as seen by the guest so while wall-clock time may be longer
+ * from the guests point of view time will pass at the normal rate.
+ *
+ * This uses the new plugin API which allows the plugin to control
+ * system time.
+ *
+ * Copyright (c) 2023 Linaro Ltd
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include <stdio.h>
+#include <glib.h>
+#include <qemu-plugin.h>
+
+QEMU_PLUGIN_EXPORT int qemu_plugin_version = QEMU_PLUGIN_VERSION;
+
+/* how many times do we update time per sec */
+#define NUM_TIME_UPDATE_PER_SEC 10
+#define NSEC_IN_ONE_SEC (1000 * 1000 * 1000)
+
+static GMutex global_state_lock;
+
+static uint64_t max_insn_per_second = 1000 * 1000 * 1000; /* ips per core, per second */
+static uint64_t max_insn_per_quantum; /* trap every N instructions */
+static int64_t virtual_time_ns; /* last set virtual time */
+
+static const void *time_handle;
+
+typedef struct {
+    uint64_t total_insn;
+    uint64_t quantum_insn; /* insn in last quantum */
+    int64_t last_quantum_time; /* time when last quantum started */
+} vCPUTime;
+
+struct qemu_plugin_scoreboard *vcpus;
+
+/* return epoch time in ns */
+static int64_t now_ns(void)
+{
+    return g_get_real_time() * 1000;
+}
+
+static uint64_t num_insn_during(int64_t elapsed_ns)
+{
+    double num_secs = elapsed_ns / (double) NSEC_IN_ONE_SEC;
+    return num_secs * (double) max_insn_per_second;
+}
+
+static int64_t time_for_insn(uint64_t num_insn)
+{
+    double num_secs = (double) num_insn / (double) max_insn_per_second;
+    return num_secs * (double) NSEC_IN_ONE_SEC;
+}
+
+static void update_system_time(vCPUTime *vcpu)
+{
+    int64_t elapsed_ns = now_ns() - vcpu->last_quantum_time;
+    uint64_t max_insn = num_insn_during(elapsed_ns);
+
+    if (vcpu->quantum_insn >= max_insn) {
+        /* this vcpu ran faster than expected, so it has to sleep */
+        uint64_t insn_advance = vcpu->quantum_insn - max_insn;
+        uint64_t time_advance_ns = time_for_insn(insn_advance);
+        int64_t sleep_us = time_advance_ns / 1000;
+        g_usleep(sleep_us);
+    }
+
+    vcpu->total_insn += vcpu->quantum_insn;
+    vcpu->quantum_insn = 0;
+    vcpu->last_quantum_time = now_ns();
+
+    /* based on total number of instructions, what should be the new time? */
+    int64_t new_virtual_time = time_for_insn(vcpu->total_insn);
+
+    g_mutex_lock(&global_state_lock);
+
+    /* Time only moves forward. Another vcpu might have updated it already. */
+    if (new_virtual_time > virtual_time_ns) {
+        qemu_plugin_update_ns(time_handle, new_virtual_time);
+        virtual_time_ns = new_virtual_time;
+    }
+
+    g_mutex_unlock(&global_state_lock);
+}
+
+static void vcpu_init(qemu_plugin_id_t id, unsigned int cpu_index)
+{
+    vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus, cpu_index);
+    vcpu->total_insn = 0;
+    vcpu->quantum_insn = 0;
+    vcpu->last_quantum_time = now_ns();
+}
+
+static void vcpu_exit(qemu_plugin_id_t id, unsigned int cpu_index)
+{
+    vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus, cpu_index);
+    update_system_time(vcpu);
+}
+
+static void every_quantum_insn(unsigned int cpu_index, void *udata)
+{
+    vCPUTime *vcpu = qemu_plugin_scoreboard_find(vcpus, cpu_index);
+    g_assert(vcpu->quantum_insn >= max_insn_per_quantum);
+    update_system_time(vcpu);
+}
+
+static void vcpu_tb_trans(qemu_plugin_id_t id, struct qemu_plugin_tb *tb)
+{
+    size_t n_insns = qemu_plugin_tb_n_insns(tb);
+    qemu_plugin_u64 quantum_insn =
+        qemu_plugin_scoreboard_u64_in_struct(vcpus, vCPUTime, quantum_insn);
+    /* count (and eventually trap) once per tb */
+    qemu_plugin_register_vcpu_tb_exec_inline_per_vcpu(
+        tb, QEMU_PLUGIN_INLINE_ADD_U64, quantum_insn, n_insns);
+    qemu_plugin_register_vcpu_tb_exec_cond_cb(
+        tb, every_quantum_insn,
+        QEMU_PLUGIN_CB_NO_REGS, QEMU_PLUGIN_COND_GE,
+        quantum_insn, max_insn_per_quantum, NULL);
+}
+
+static void plugin_exit(qemu_plugin_id_t id, void *udata)
+{
+    qemu_plugin_scoreboard_free(vcpus);
+}
+
+QEMU_PLUGIN_EXPORT int qemu_plugin_install(qemu_plugin_id_t id,
+                                           const qemu_info_t *info, int argc,
+                                           char **argv)
+{
+    for (int i = 0; i < argc; i++) {
+        char *opt = argv[i];
+        g_auto(GStrv) tokens = g_strsplit(opt, "=", 2);
+        if (g_strcmp0(tokens[0], "ips") == 0) {
+            max_insn_per_second = g_ascii_strtoull(tokens[1], NULL, 10);
+            if (!max_insn_per_second && errno) {
+                fprintf(stderr, "%s: couldn't parse %s (%s)\n",
+                        __func__, tokens[1], g_strerror(errno));
+                return -1;
+            }
+        } else {
+            fprintf(stderr, "option parsing failed: %s\n", opt);
+            return -1;
+        }
+    }
+
+    vcpus = qemu_plugin_scoreboard_new(sizeof(vCPUTime));
+    max_insn_per_quantum = max_insn_per_second / NUM_TIME_UPDATE_PER_SEC;
+
+    time_handle = qemu_plugin_request_time_control();
+    g_assert(time_handle);
+
+    qemu_plugin_register_vcpu_tb_trans_cb(id, vcpu_tb_trans);
+    qemu_plugin_register_vcpu_init_cb(id, vcpu_init);
+    qemu_plugin_register_vcpu_exit_cb(id, vcpu_exit);
+    qemu_plugin_register_atexit_cb(id, plugin_exit, NULL);
+
+    return 0;
+}