[PATCH v4 28/33] vfio/migration: Multifd device state transfer support - load thread

[Maciej S. Szmigiero]

From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>

Since it's important to finish loading device state transferred via the
main migration channel (via save_live_iterate SaveVMHandler) before
starting loading the data asynchronously transferred via multifd the thread
doing the actual loading of the multifd transferred data is only started
from switchover_start SaveVMHandler.

switchover_start handler is called when MIG_CMD_SWITCHOVER_START
sub-command of QEMU_VM_COMMAND is received via the main migration channel.

This sub-command is only sent after all save_live_iterate data have already
been posted so it is safe to commence loading of the multifd-transferred
device state upon receiving it - loading of save_live_iterate data happens
synchronously in the main migration thread (much like the processing of
MIG_CMD_SWITCHOVER_START) so by the time MIG_CMD_SWITCHOVER_START is
processed all the proceeding data must have already been loaded.

Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
---
 hw/vfio/migration.c  | 229 +++++++++++++++++++++++++++++++++++++++++++
 hw/vfio/trace-events |   5 +
 2 files changed, 234 insertions(+)

diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
index 0c0caec1bd64..ab5b097f59c9 100644
--- a/hw/vfio/migration.c
+++ b/hw/vfio/migration.c
@@ -301,8 +301,16 @@ typedef struct VFIOStateBuffer {
 } VFIOStateBuffer;
 
 typedef struct VFIOMultifd {
+    QemuThread load_bufs_thread;
+    bool load_bufs_thread_running;
+    bool load_bufs_thread_want_exit;
+
+    bool load_bufs_iter_done;
+    QemuCond load_bufs_iter_done_cond;
+
     VFIOStateBuffers load_bufs;
     QemuCond load_bufs_buffer_ready_cond;
+    QemuCond load_bufs_thread_finished_cond;
     QemuMutex load_bufs_mutex; /* Lock order: this lock -> BQL */
     uint32_t load_buf_idx;
     uint32_t load_buf_idx_last;
@@ -449,6 +457,171 @@ static bool vfio_load_state_buffer(void *opaque, char 
*data, size_t data_size,
     return true;
 }
 
+static VFIOStateBuffer *vfio_load_state_buffer_get(VFIOMultifd *multifd)
+{
+    VFIOStateBuffer *lb;
+    guint bufs_len;
+
+    bufs_len = vfio_state_buffers_size_get(&multifd->load_bufs);
+    if (multifd->load_buf_idx >= bufs_len) {
+        assert(multifd->load_buf_idx == bufs_len);
+        return NULL;
+    }
+
+    lb = vfio_state_buffers_at(&multifd->load_bufs,
+                               multifd->load_buf_idx);
+    if (!lb->is_present) {
+        return NULL;
+    }
+
+    return lb;
+}
+
+static int vfio_load_bufs_thread_load_config(VFIODevice *vbasedev)
+{
+    return -EINVAL;
+}
+
+static bool vfio_load_state_buffer_write(VFIODevice *vbasedev,
+                                         VFIOStateBuffer *lb,
+                                         Error **errp)
+{
+    VFIOMigration *migration = vbasedev->migration;
+    VFIOMultifd *multifd = migration->multifd;
+    g_autofree char *buf = NULL;
+    char *buf_cur;
+    size_t buf_len;
+
+    if (!lb->len) {
+        return true;
+    }
+
+    trace_vfio_load_state_device_buffer_load_start(vbasedev->name,
+                                                   multifd->load_buf_idx);
+
+    /* lb might become re-allocated when we drop the lock */
+    buf = g_steal_pointer(&lb->data);
+    buf_cur = buf;
+    buf_len = lb->len;
+    while (buf_len > 0) {
+        ssize_t wr_ret;
+        int errno_save;
+
+        /*
+         * Loading data to the device takes a while,
+         * drop the lock during this process.
+         */
+        qemu_mutex_unlock(&multifd->load_bufs_mutex);
+        wr_ret = write(migration->data_fd, buf_cur, buf_len);
+        errno_save = errno;
+        qemu_mutex_lock(&multifd->load_bufs_mutex);
+
+        if (wr_ret < 0) {
+            error_setg(errp,
+                       "writing state buffer %" PRIu32 " failed: %d",
+                       multifd->load_buf_idx, errno_save);
+            return false;
+        }
+
+        assert(wr_ret <= buf_len);
+        buf_len -= wr_ret;
+        buf_cur += wr_ret;
+    }
+
+    trace_vfio_load_state_device_buffer_load_end(vbasedev->name,
+                                                 multifd->load_buf_idx);
+
+    return true;
+}
+
+static bool vfio_load_bufs_thread_want_abort(VFIOMultifd *multifd,
+                                             bool *should_quit)
+{
+    return multifd->load_bufs_thread_want_exit || qatomic_read(should_quit);
+}
+
+static bool vfio_load_bufs_thread(void *opaque, bool *should_quit, Error 
**errp)
+{
+    VFIODevice *vbasedev = opaque;
+    VFIOMigration *migration = vbasedev->migration;
+    VFIOMultifd *multifd = migration->multifd;
+    bool ret = true;
+    int config_ret;
+
+    assert(multifd);
+    QEMU_LOCK_GUARD(&multifd->load_bufs_mutex);
+
+    assert(multifd->load_bufs_thread_running);
+
+    while (!vfio_load_bufs_thread_want_abort(multifd, should_quit)) {
+        VFIOStateBuffer *lb;
+
+        assert(multifd->load_buf_idx <= multifd->load_buf_idx_last);
+
+        lb = vfio_load_state_buffer_get(multifd);
+        if (!lb) {
+            trace_vfio_load_state_device_buffer_starved(vbasedev->name,
+                                                        multifd->load_buf_idx);
+            qemu_cond_wait(&multifd->load_bufs_buffer_ready_cond,
+                           &multifd->load_bufs_mutex);
+            continue;
+        }
+
+        if (multifd->load_buf_idx == multifd->load_buf_idx_last) {
+            break;
+        }
+
+        if (multifd->load_buf_idx == 0) {
+            trace_vfio_load_state_device_buffer_start(vbasedev->name);
+        }
+
+        if (!vfio_load_state_buffer_write(vbasedev, lb, errp)) {
+            ret = false;
+            goto ret_signal;
+        }
+
+        assert(multifd->load_buf_queued_pending_buffers > 0);
+        multifd->load_buf_queued_pending_buffers--;
+
+        if (multifd->load_buf_idx == multifd->load_buf_idx_last - 1) {
+            trace_vfio_load_state_device_buffer_end(vbasedev->name);
+        }
+
+        multifd->load_buf_idx++;
+    }
+
+    if (vfio_load_bufs_thread_want_abort(multifd, should_quit)) {
+        error_setg(errp, "operation cancelled");
+        ret = false;
+        goto ret_signal;
+    }
+
+    if (vfio_load_config_after_iter(vbasedev)) {
+        while (!multifd->load_bufs_iter_done) {
+            qemu_cond_wait(&multifd->load_bufs_iter_done_cond,
+                           &multifd->load_bufs_mutex);
+
+            if (vfio_load_bufs_thread_want_abort(multifd, should_quit)) {
+                error_setg(errp, "operation cancelled");
+                ret = false;
+                goto ret_signal;
+            }
+        }
+    }
+
+    config_ret = vfio_load_bufs_thread_load_config(vbasedev);
+    if (config_ret) {
+        error_setg(errp, "load config state failed: %d", config_ret);
+        ret = false;
+    }
+
+ret_signal:
+    multifd->load_bufs_thread_running = false;
+    qemu_cond_signal(&multifd->load_bufs_thread_finished_cond);
+
+    return ret;
+}
+
 static int vfio_save_device_config_state(QEMUFile *f, void *opaque,
                                          Error **errp)
 {
@@ -517,11 +690,40 @@ static VFIOMultifd *vfio_multifd_new(void)
     multifd->load_buf_queued_pending_buffers = 0;
     qemu_cond_init(&multifd->load_bufs_buffer_ready_cond);
 
+    multifd->load_bufs_iter_done = false;
+    qemu_cond_init(&multifd->load_bufs_iter_done_cond);
+
+    multifd->load_bufs_thread_running = false;
+    multifd->load_bufs_thread_want_exit = false;
+    qemu_cond_init(&multifd->load_bufs_thread_finished_cond);
+
     return multifd;
 }
 
+static void vfio_load_cleanup_load_bufs_thread(VFIOMultifd *multifd)
+{
+    /* The lock order is load_bufs_mutex -> BQL so unlock BQL here first */
+    bql_unlock();
+    WITH_QEMU_LOCK_GUARD(&multifd->load_bufs_mutex) {
+        while (multifd->load_bufs_thread_running) {
+            multifd->load_bufs_thread_want_exit = true;
+
+            qemu_cond_signal(&multifd->load_bufs_buffer_ready_cond);
+            qemu_cond_signal(&multifd->load_bufs_iter_done_cond);
+            qemu_cond_wait(&multifd->load_bufs_thread_finished_cond,
+                           &multifd->load_bufs_mutex);
+        }
+    }
+    bql_lock();
+}
+
 static void vfio_multifd_free(VFIOMultifd *multifd)
 {
+    vfio_load_cleanup_load_bufs_thread(multifd);
+
+    qemu_cond_destroy(&multifd->load_bufs_thread_finished_cond);
+    qemu_cond_destroy(&multifd->load_bufs_iter_done_cond);
+    vfio_state_buffers_destroy(&multifd->load_bufs);
     qemu_cond_destroy(&multifd->load_bufs_buffer_ready_cond);
     qemu_mutex_destroy(&multifd->load_bufs_mutex);
 
@@ -1042,6 +1244,32 @@ static bool vfio_switchover_ack_needed(void *opaque)
     return vfio_precopy_supported(vbasedev);
 }
 
+static int vfio_switchover_start(void *opaque)
+{
+    VFIODevice *vbasedev = opaque;
+    VFIOMigration *migration = vbasedev->migration;
+    VFIOMultifd *multifd = migration->multifd;
+
+    if (!migration->multifd_transfer) {
+        /* Load thread is only used for multifd transfer */
+        return 0;
+    }
+
+    assert(multifd);
+
+    /* The lock order is load_bufs_mutex -> BQL so unlock BQL here first */
+    bql_unlock();
+    WITH_QEMU_LOCK_GUARD(&multifd->load_bufs_mutex) {
+        assert(!multifd->load_bufs_thread_running);
+        multifd->load_bufs_thread_running = true;
+    }
+    bql_lock();
+
+    qemu_loadvm_start_load_thread(vfio_load_bufs_thread, vbasedev);
+
+    return 0;
+}
+
 static const SaveVMHandlers savevm_vfio_handlers = {
     .save_prepare = vfio_save_prepare,
     .save_setup = vfio_save_setup,
@@ -1057,6 +1285,7 @@ static const SaveVMHandlers savevm_vfio_handlers = {
     .load_state = vfio_load_state,
     .load_state_buffer = vfio_load_state_buffer,
     .switchover_ack_needed = vfio_switchover_ack_needed,
+    .switchover_start = vfio_switchover_start,
 };
 
 /* ---------------------------------------------------------------------- */
diff --git a/hw/vfio/trace-events b/hw/vfio/trace-events
index 042a3dc54a33..418b378ebd29 100644
--- a/hw/vfio/trace-events
+++ b/hw/vfio/trace-events
@@ -154,6 +154,11 @@ vfio_load_device_config_state_end(const char *name) " (%s)"
 vfio_load_state(const char *name, uint64_t data) " (%s) data 0x%"PRIx64
 vfio_load_state_device_data(const char *name, uint64_t data_size, int ret) " 
(%s) size %"PRIu64" ret %d"
 vfio_load_state_device_buffer_incoming(const char *name, uint32_t idx) " (%s) 
idx %"PRIu32
+vfio_load_state_device_buffer_start(const char *name) " (%s)"
+vfio_load_state_device_buffer_starved(const char *name, uint32_t idx) " (%s) 
idx %"PRIu32
+vfio_load_state_device_buffer_load_start(const char *name, uint32_t idx) " 
(%s) idx %"PRIu32
+vfio_load_state_device_buffer_load_end(const char *name, uint32_t idx) " (%s) 
idx %"PRIu32
+vfio_load_state_device_buffer_end(const char *name) " (%s)"
 vfio_migration_realize(const char *name) " (%s)"
 vfio_migration_set_device_state(const char *name, const char *state) " (%s) 
state %s"
 vfio_migration_set_state(const char *name, const char *new_state, const char 
*recover_state) " (%s) new state %s, recover state %s"