5 files changed, 27 insertions, 0 deletions

diff --git a/drivers/lguest/lguest_device.c b/drivers/lguest/lguest_device.c
index 54fdc2aa4806..37344aaee22f 100644
--- a/drivers/lguest/lguest_device.c
+++ b/drivers/lguest/lguest_device.c
@@ -105,6 +105,9 @@ static void lg_finalize_features(struct virtio_device *vdev)
         /* Second half of bitmap is features we accept. */
         u8 *out_features = lg_features(desc) + desc->feature_len;
 
+        /* Give virtio_ring a chance to accept features. */
+        vring_transport_features(vdev);
+
         memset(out_features, 0, desc->feature_len);
         bits = min_t(unsigned, desc->feature_len, sizeof(vdev->features)) * 8;
         for (i = 0; i < bits; i++) {
diff --git a/drivers/s390/kvm/kvm_virtio.c b/drivers/s390/kvm/kvm_virtio.c
index 5953510e7d5f..79954bd6bfa5 100644
--- a/drivers/s390/kvm/kvm_virtio.c
+++ b/drivers/s390/kvm/kvm_virtio.c
@@ -95,6 +95,9 @@ static void kvm_finalize_features(struct virtio_device *vdev)
         /* Second half of bitmap is features we accept. */
         u8 *out_features = kvm_vq_features(desc) + desc->feature_len;
 
+        /* Give virtio_ring a chance to accept features. */
+        vring_transport_features(vdev);
+
         memset(out_features, 0, desc->feature_len);
         bits = min_t(unsigned, desc->feature_len, sizeof(vdev->features)) * 8;
         for (i = 0; i < bits; i++) {
diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
index 9855975a72a3..c7dc37c7cce9 100644
--- a/drivers/virtio/virtio_pci.c
+++ b/drivers/virtio/virtio_pci.c
@@ -99,6 +99,9 @@ static void vp_finalize_features(struct virtio_device *vdev)
 {
         struct virtio_pci_device *vp_dev = to_vp_device(vdev);
 
+        /* Give virtio_ring a chance to accept features. */
+        vring_transport_features(vdev);
+
         /* We only support 32 feature bits. */
         BUILD_BUG_ON(ARRAY_SIZE(vdev->features) != 1);
         iowrite32(vdev->features[0], vp_dev->ioaddr+VIRTIO_PCI_GUEST_FEATURES);
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 21d9a62767af..6eb5303fed11 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -18,6 +18,7 @@
  */
 #include <linux/virtio.h>
 #include <linux/virtio_ring.h>
+#include <linux/virtio_config.h>
 #include <linux/device.h>
 
 #ifdef DEBUG
@@ -323,4 +324,19 @@ void vring_del_virtqueue(struct virtqueue *vq)
 }
 EXPORT_SYMBOL_GPL(vring_del_virtqueue);
 
+/* Manipulates transport-specific feature bits. */
+void vring_transport_features(struct virtio_device *vdev)
+{
+        unsigned int i;
+
+        for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++) {
+                switch (i) {
+                default:
+                        /* We don't understand this bit. */
+                        clear_bit(i, vdev->features);
+                }
+        }
+}
+EXPORT_SYMBOL_GPL(vring_transport_features);
+
 MODULE_LICENSE("GPL");
diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index abe481ed990e..c4a598fb3826 100644
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h
@@ -120,6 +120,8 @@ struct virtqueue *vring_new_virtqueue(unsigned int num,
                                       void (*notify)(struct virtqueue *vq),
                                       void (*callback)(struct virtqueue *vq));
 void vring_del_virtqueue(struct virtqueue *vq);
+/* Filter out transport-specific feature bits. */
+void vring_transport_features(struct virtio_device *vdev);
 
 irqreturn_t vring_interrupt(int irq, void *_vq);
 #endif /* __KERNEL__ */