virtio: add legacy feature table support

virtio-blk has some legacy feature bits that modern drivers
must not negotiate, but are needed for old legacy hosts
(that e.g. don't support virtio-scsi).
Allow a separate legacy feature table for such cases.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>

2 files changed, 28 insertions, 1 deletions

diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index 3e78f4bcfa8e..f9ad99c8b352 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -113,6 +113,13 @@ void virtio_check_driver_offered_feature(const struct virtio_device *vdev,
         for (i = 0; i < drv->feature_table_size; i++)
                 if (drv->feature_table[i] == fbit)
                         return;
+
+        if (drv->feature_table_legacy) {
+                for (i = 0; i < drv->feature_table_size_legacy; i++)
+                        if (drv->feature_table_legacy[i] == fbit)
+                                return;
+        }
+
         BUG();
 }
 EXPORT_SYMBOL_GPL(virtio_check_driver_offered_feature);
@@ -161,6 +168,7 @@ static int virtio_dev_probe(struct device *_d)
         struct virtio_driver *drv = drv_to_virtio(dev->dev.driver);
         u64 device_features;
         u64 driver_features;
+        u64 driver_features_legacy;
         unsigned status;
 
         /* We have a driver! */
@@ -177,7 +185,22 @@ static int virtio_dev_probe(struct device *_d)
                 driver_features |= (1ULL << f);
         }
 
-        dev->features = driver_features & device_features;
+        /* Some drivers have a separate feature table for virtio v1.0 */
+        if (drv->feature_table_legacy) {
+                driver_features_legacy = 0;
+                for (i = 0; i < drv->feature_table_size_legacy; i++) {
+                        unsigned int f = drv->feature_table_legacy[i];
+                        BUG_ON(f >= 64);
+                        driver_features_legacy |= (1ULL << f);
+                }
+        } else {
+                driver_features_legacy = driver_features;
+        }
+
+        if (driver_features & device_features & (1ULL << VIRTIO_F_VERSION_1))
+                dev->features = driver_features & device_features;
+        else
+                dev->features = driver_features_legacy & device_features;
 
         /* Transport features always preserved to pass to finalize_features. */
         for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++)
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index d6359a5d5d4e..f70411eb9d27 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -130,6 +130,8 @@ int virtio_device_restore(struct virtio_device *dev);
  * @id_table: the ids serviced by this driver.
  * @feature_table: an array of feature numbers supported by this driver.
  * @feature_table_size: number of entries in the feature table array.
+ * @feature_table_legacy: same as feature_table but when working in legacy mode.
+ * @feature_table_size_legacy: number of entries in feature table legacy array.
  * @probe: the function to call when a device is found.  Returns 0 or -errno.
  * @remove: the function to call when a device is removed.
  * @config_changed: optional function to call when the device configuration
@@ -140,6 +142,8 @@ struct virtio_driver {
         const struct virtio_device_id *id_table;
         const unsigned int *feature_table;
         unsigned int feature_table_size;
+        const unsigned int *feature_table_legacy;
+        unsigned int feature_table_size_legacy;
         int (*probe)(struct virtio_device *dev);
         void (*scan)(struct virtio_device *dev);
         void (*remove)(struct virtio_device *dev);