vhost: Add Shadow VirtQueue kick forwarding capabilities

At this mode no buffer forwarding will be performed in SVQ mode: Qemu
will just forward the guest's kicks to the device.

Host memory notifiers regions are left out for simplicity, and they will
not be addressed in this series.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

hw/virtio/vhost-shadow-virtqueue.c

@@ -11,6 +11,59 @@
 #include "hw/virtio/vhost-shadow-virtqueue.h"
 
 #include "qemu/error-report.h"
+#include "qemu/main-loop.h"
+#include "linux-headers/linux/vhost.h"
+
+/**
+ * Forward guest notifications.
+ *
+ * @n: guest kick event notifier, the one that guest set to notify svq.
+ */
+static void vhost_handle_guest_kick(EventNotifier *n)
+{
+    VhostShadowVirtqueue *svq = container_of(n, VhostShadowVirtqueue, svq_kick);
+    event_notifier_test_and_clear(n);
+    event_notifier_set(&svq->hdev_kick);
+}
+
+/**
+ * Set a new file descriptor for the guest to kick the SVQ and notify for avail
+ *
+ * @svq: The svq
+ * @svq_kick_fd: The svq kick fd
+ *
+ * Note that the SVQ will never close the old file descriptor.
+ */
+void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, int svq_kick_fd)
+{
+    EventNotifier *svq_kick = &svq->svq_kick;
+    bool poll_stop = VHOST_FILE_UNBIND != event_notifier_get_fd(svq_kick);
+    bool poll_start = svq_kick_fd != VHOST_FILE_UNBIND;
+
+    if (poll_stop) {
+        event_notifier_set_handler(svq_kick, NULL);
+    }
+
+    /*
+     * event_notifier_set_handler already checks for guest's notifications if
+     * they arrive at the new file descriptor in the switch, so there is no
+     * need to explicitly check for them.
+     */
+    if (poll_start) {
+        event_notifier_init_fd(svq_kick, svq_kick_fd);
+        event_notifier_set(svq_kick);
+        event_notifier_set_handler(svq_kick, vhost_handle_guest_kick);
+    }
+}
+
+/**
+ * Stop the shadow virtqueue operation.
+ * @svq: Shadow Virtqueue
+ */
+void vhost_svq_stop(VhostShadowVirtqueue *svq)
+{
+    event_notifier_set_handler(&svq->svq_kick, NULL);
+}
 
 /**
  * Creates vhost shadow virtqueue, and instructs the vhost device to use the
@@ -39,6 +92,7 @@ VhostShadowVirtqueue *vhost_svq_new(void)
         goto err_init_hdev_call;
     }
 
+    event_notifier_init_fd(&svq->svq_kick, VHOST_FILE_UNBIND);
     return g_steal_pointer(&svq);
 
 err_init_hdev_call:
@@ -56,6 +110,7 @@ err_init_hdev_kick:
 void vhost_svq_free(gpointer pvq)
 {
     VhostShadowVirtqueue *vq = pvq;
+    vhost_svq_stop(vq);
     event_notifier_cleanup(&vq->hdev_kick);
     event_notifier_cleanup(&vq->hdev_call);
     g_free(vq);

hw/virtio/vhost-shadow-virtqueue.h

@@ -18,8 +18,22 @@ typedef struct VhostShadowVirtqueue {
     EventNotifier hdev_kick;
     /* Shadow call notifier, sent to vhost */
     EventNotifier hdev_call;
+
+    /*
+     * Borrowed virtqueue's guest to host notifier. To borrow it in this event
+     * notifier allows to recover the VhostShadowVirtqueue from the event loop
+     * easily. If we use the VirtQueue's one, we don't have an easy way to
+     * retrieve VhostShadowVirtqueue.
+     *
+     * So shadow virtqueue must not clean it, or we would lose VirtQueue one.
+     */
+    EventNotifier svq_kick;
 } VhostShadowVirtqueue;
 
+void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, int svq_kick_fd);
+
+void vhost_svq_stop(VhostShadowVirtqueue *svq);
+
 VhostShadowVirtqueue *vhost_svq_new(void);
 
 void vhost_svq_free(gpointer vq);

hw/virtio/vhost-vdpa.c

@@ -17,12 +17,14 @@
 #include "hw/virtio/vhost.h"
 #include "hw/virtio/vhost-backend.h"
 #include "hw/virtio/virtio-net.h"
+#include "hw/virtio/vhost-shadow-virtqueue.h"
 #include "hw/virtio/vhost-vdpa.h"
 #include "exec/address-spaces.h"
 #include "qemu/main-loop.h"
 #include "cpu.h"
 #include "trace.h"
 #include "qemu-common.h"
+#include "qapi/error.h"
 
 /*
  * Return one past the end of the end of section. Be careful with uint64_t
@@ -342,6 +344,30 @@ static bool vhost_vdpa_one_time_request(struct vhost_dev *dev)
     return v->index != 0;
 }
 
+static int vhost_vdpa_init_svq(struct vhost_dev *hdev, struct vhost_vdpa *v,
+                               Error **errp)
+{
+    g_autoptr(GPtrArray) shadow_vqs = NULL;
+
+    if (!v->shadow_vqs_enabled) {
+        return 0;
+    }
+
+    shadow_vqs = g_ptr_array_new_full(hdev->nvqs, vhost_svq_free);
+    for (unsigned n = 0; n < hdev->nvqs; ++n) {
+        g_autoptr(VhostShadowVirtqueue) svq = vhost_svq_new();
+
+        if (unlikely(!svq)) {
+            error_setg(errp, "Cannot create svq %u", n);
+            return -1;
+        }
+        g_ptr_array_add(shadow_vqs, g_steal_pointer(&svq));
+    }
+
+    v->shadow_vqs = g_steal_pointer(&shadow_vqs);
+    return 0;
+}
+
 static int vhost_vdpa_init(struct vhost_dev *dev, void *opaque, Error **errp)
 {
     struct vhost_vdpa *v;
@@ -364,6 +390,10 @@ static int vhost_vdpa_init(struct vhost_dev *dev, void *opaque, Error **errp)
     dev->opaque =  opaque ;
     v->listener = vhost_vdpa_memory_listener;
     v->msg_type = VHOST_IOTLB_MSG_V2;
+    ret = vhost_vdpa_init_svq(dev, v, errp);
+    if (ret) {
+        goto err;
+    }
 
     vhost_vdpa_get_iova_range(v);
 
@@ -375,6 +405,10 @@ static int vhost_vdpa_init(struct vhost_dev *dev, void *opaque, Error **errp)
                                VIRTIO_CONFIG_S_DRIVER);
 
     return 0;
+
+err:
+    ram_block_discard_disable(false);
+    return ret;
 }
 
 static void vhost_vdpa_host_notifier_uninit(struct vhost_dev *dev,
@@ -445,8 +479,14 @@ static void vhost_vdpa_host_notifiers_uninit(struct vhost_dev *dev, int n)
 
 static void vhost_vdpa_host_notifiers_init(struct vhost_dev *dev)
 {
+    struct vhost_vdpa *v = dev->opaque;
     int i;
 
+    if (v->shadow_vqs_enabled) {
+        /* FIXME SVQ is not compatible with host notifiers mr */
+        return;
+    }
+
     for (i = dev->vq_index; i < dev->vq_index + dev->nvqs; i++) {
         if (vhost_vdpa_host_notifier_init(dev, i)) {
             goto err;
@@ -460,6 +500,21 @@ err:
     return;
 }
 
+static void vhost_vdpa_svq_cleanup(struct vhost_dev *dev)
+{
+    struct vhost_vdpa *v = dev->opaque;
+    size_t idx;
+
+    if (!v->shadow_vqs) {
+        return;
+    }
+
+    for (idx = 0; idx < v->shadow_vqs->len; ++idx) {
+        vhost_svq_stop(g_ptr_array_index(v->shadow_vqs, idx));
+    }
+    g_ptr_array_free(v->shadow_vqs, true);
+}
+
 static int vhost_vdpa_cleanup(struct vhost_dev *dev)
 {
     struct vhost_vdpa *v;
@@ -468,6 +523,7 @@ static int vhost_vdpa_cleanup(struct vhost_dev *dev)
     trace_vhost_vdpa_cleanup(dev, v);
     vhost_vdpa_host_notifiers_uninit(dev, dev->nvqs);
     memory_listener_unregister(&v->listener);
+    vhost_vdpa_svq_cleanup(dev);
 
     dev->opaque = NULL;
     ram_block_discard_disable(false);
@@ -559,11 +615,26 @@ static int vhost_vdpa_get_device_id(struct vhost_dev *dev,
     return ret;
 }
 
+static void vhost_vdpa_reset_svq(struct vhost_vdpa *v)
+{
+    if (!v->shadow_vqs_enabled) {
+        return;
+    }
+
+    for (unsigned i = 0; i < v->shadow_vqs->len; ++i) {
+        VhostShadowVirtqueue *svq = g_ptr_array_index(v->shadow_vqs, i);
+        vhost_svq_stop(svq);
+    }
+}
+
 static int vhost_vdpa_reset_device(struct vhost_dev *dev)
 {
+    struct vhost_vdpa *v = dev->opaque;
     int ret;
     uint8_t status = 0;
 
+    vhost_vdpa_reset_svq(v);
+
     ret = vhost_vdpa_call(dev, VHOST_VDPA_SET_STATUS, &status);
     trace_vhost_vdpa_reset_device(dev, status);
     return ret;
@@ -647,13 +718,74 @@ static int vhost_vdpa_get_config(struct vhost_dev *dev, uint8_t *config,
     return ret;
  }
 
+static int vhost_vdpa_set_vring_dev_kick(struct vhost_dev *dev,
+                                         struct vhost_vring_file *file)
+{
+    trace_vhost_vdpa_set_vring_kick(dev, file->index, file->fd);
+    return vhost_vdpa_call(dev, VHOST_SET_VRING_KICK, file);
+}
+
+/**
+ * Set the shadow virtqueue descriptors to the device
+ *
+ * @dev: The vhost device model
+ * @svq: The shadow virtqueue
+ * @idx: The index of the virtqueue in the vhost device
+ * @errp: Error
+ */
+static bool vhost_vdpa_svq_setup(struct vhost_dev *dev,
+                                 VhostShadowVirtqueue *svq, unsigned idx,
+                                 Error **errp)
+{
+    struct vhost_vring_file file = {
+        .index = dev->vq_index + idx,
+    };
+    const EventNotifier *event_notifier = &svq->hdev_kick;
+    int r;
+
+    file.fd = event_notifier_get_fd(event_notifier);
+    r = vhost_vdpa_set_vring_dev_kick(dev, &file);
+    if (unlikely(r != 0)) {
+        error_setg_errno(errp, -r, "Can't set device kick fd");
+    }
+
+    return r == 0;
+}
+
+static bool vhost_vdpa_svqs_start(struct vhost_dev *dev)
+{
+    struct vhost_vdpa *v = dev->opaque;
+    Error *err = NULL;
+    unsigned i;
+
+    if (!v->shadow_vqs) {
+        return true;
+    }
+
+    for (i = 0; i < v->shadow_vqs->len; ++i) {
+        VhostShadowVirtqueue *svq = g_ptr_array_index(v->shadow_vqs, i);
+        bool ok = vhost_vdpa_svq_setup(dev, svq, i, &err);
+        if (unlikely(!ok)) {
+            error_reportf_err(err, "Cannot setup SVQ %u: ", i);
+            return false;
+        }
+    }
+
+    return true;
+}
+
 static int vhost_vdpa_dev_start(struct vhost_dev *dev, bool started)
 {
     struct vhost_vdpa *v = dev->opaque;
+    bool ok;
     trace_vhost_vdpa_dev_start(dev, started);
 
     if (started) {
         vhost_vdpa_host_notifiers_init(dev);
+        ok = vhost_vdpa_svqs_start(dev);
+        if (unlikely(!ok)) {
+            return -1;
+        }
         vhost_vdpa_set_vring_ready(dev);
     } else {
         vhost_vdpa_host_notifiers_uninit(dev, dev->nvqs);
@@ -725,8 +857,16 @@ static int vhost_vdpa_get_vring_base(struct vhost_dev *dev,
 static int vhost_vdpa_set_vring_kick(struct vhost_dev *dev,
                                        struct vhost_vring_file *file)
 {
-    trace_vhost_vdpa_set_vring_kick(dev, file->index, file->fd);
-    return vhost_vdpa_call(dev, VHOST_SET_VRING_KICK, file);
+    struct vhost_vdpa *v = dev->opaque;
+    int vdpa_idx = file->index - dev->vq_index;
+
+    if (v->shadow_vqs_enabled) {
+        VhostShadowVirtqueue *svq = g_ptr_array_index(v->shadow_vqs, vdpa_idx);
+        vhost_svq_set_svq_kick_fd(svq, file->fd);
+        return 0;
+    } else {
+        return vhost_vdpa_set_vring_dev_kick(dev, file);
+    }
 }
 
 static int vhost_vdpa_set_vring_call(struct vhost_dev *dev,

include/hw/virtio/vhost-vdpa.h

@@ -12,6 +12,8 @@
 #ifndef HW_VIRTIO_VHOST_VDPA_H
 #define HW_VIRTIO_VHOST_VDPA_H
 
+#include <gmodule.h>
+
 #include "hw/virtio/virtio.h"
 #include "standard-headers/linux/vhost_types.h"
 
@@ -27,6 +29,8 @@ typedef struct vhost_vdpa {
     bool iotlb_batch_begin_sent;
     MemoryListener listener;
     struct vhost_vdpa_iova_range iova_range;
+    bool shadow_vqs_enabled;
+    GPtrArray *shadow_vqs;
     struct vhost_dev *dev;
     VhostVDPAHostNotifier notifier[VIRTIO_QUEUE_MAX];
 } VhostVDPA;