virtio: Allow .get_vhost() without vhost_started

Historically, .get_vhost() was probably only called when
vdev->vhost_started is true.  However, we now decidedly want to call it
also when vhost_started is false, specifically so we can issue a reset
to the vhost back-end while device operation is stopped.

Some .get_vhost() implementations dereference some pointers (or return
offsets from them) that are probably guaranteed to be non-NULL when
vhost_started is true, but not necessarily otherwise.  This patch makes
all such implementations check all such pointers, returning NULL if any
is NULL.

Signed-off-by: Hanna Czenczek <hreitz@redhat.com>
Message-Id: <20240723163941.48775-2-hreitz@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

hw/display/vhost-user-gpu.c

@@ -642,7 +642,7 @@ vhost_user_gpu_device_realize(DeviceState *qdev, Error **errp)
 static struct vhost_dev *vhost_user_gpu_get_vhost(VirtIODevice *vdev)
 {
     VhostUserGPU *g = VHOST_USER_GPU(vdev);
-    return &g->vhost->dev;
+    return g->vhost ? &g->vhost->dev : NULL;
 }
 
 static Property vhost_user_gpu_properties[] = {

hw/net/virtio-net.c

@@ -3896,8 +3896,23 @@ static bool dev_unplug_pending(void *opaque)
 static struct vhost_dev *virtio_net_get_vhost(VirtIODevice *vdev)
 {
     VirtIONet *n = VIRTIO_NET(vdev);
-    NetClientState *nc = qemu_get_queue(n->nic);
-    struct vhost_net *net = get_vhost_net(nc->peer);
+    NetClientState *nc;
+    struct vhost_net *net;
+
+    if (!n->nic) {
+        return NULL;
+    }
+
+    nc = qemu_get_queue(n->nic);
+    if (!nc) {
+        return NULL;
+    }
+
+    net = get_vhost_net(nc->peer);
+    if (!net) {
+        return NULL;
+    }
+
     return &net->dev;
 }
 

hw/virtio/virtio-crypto.c

@@ -1247,9 +1247,21 @@ static bool virtio_crypto_guest_notifier_pending(VirtIODevice *vdev, int idx)
 static struct vhost_dev *virtio_crypto_get_vhost(VirtIODevice *vdev)
 {
     VirtIOCrypto *vcrypto = VIRTIO_CRYPTO(vdev);
-    CryptoDevBackend *b = vcrypto->cryptodev;
-    CryptoDevBackendClient *cc = b->conf.peers.ccs[0];
-    CryptoDevBackendVhost *vhost_crypto = cryptodev_get_vhost(cc, b, 0);
+    CryptoDevBackend *b;
+    CryptoDevBackendClient *cc;
+    CryptoDevBackendVhost *vhost_crypto;
+
+    b = vcrypto->cryptodev;
+    if (!b) {
+        return NULL;
+    }
+
+    cc = b->conf.peers.ccs[0];
+    vhost_crypto = cryptodev_get_vhost(cc, b, 0);
+    if (!vhost_crypto) {
+        return NULL;
+    }
+
     return &vhost_crypto->dev;
 }
 

include/hw/virtio/virtio.h

@@ -223,6 +223,7 @@ struct VirtioDeviceClass {
     int (*post_load)(VirtIODevice *vdev);
     const VMStateDescription *vmsd;
     bool (*primary_unplug_pending)(void *opaque);
+    /* May be called even when vdev->vhost_started is false */
     struct vhost_dev *(*get_vhost)(VirtIODevice *vdev);
     void (*toggle_device_iotlb)(VirtIODevice *vdev);
 };