Fix oops on 2.6.25 guest (Rusty Russell)

I believe this is behind the following:
https://bugs.edge.launchpad.net/ubuntu/jaunty/+source/linux/+bug/331128

virtio_pci in 2.6.25 didn't do feature negotiation correctly: it acked every
bit.  Fortunately, we can detect this.
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>


git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6975 c046a42c-6fe2-441c-8c8c-71466251a162

hw/virtio-net.c

@@ -113,6 +113,21 @@ static uint32_t virtio_net_get_features(VirtIODevice *vdev)
     return features;
 }
 
+static uint32_t virtio_net_bad_features(VirtIODevice *vdev)
+{
+    uint32_t features = 0;
+
+    /* Linux kernel 2.6.25.  It understood MAC (as everyone must),
+     * but also these: */
+    features |= (1 << VIRTIO_NET_F_MAC);
+    features |= (1 << VIRTIO_NET_F_GUEST_CSUM);
+    features |= (1 << VIRTIO_NET_F_GUEST_TSO4);
+    features |= (1 << VIRTIO_NET_F_GUEST_TSO6);
+    features |= (1 << VIRTIO_NET_F_GUEST_ECN);
+
+    return features & virtio_net_get_features(vdev);
+}
+
 static void virtio_net_set_features(VirtIODevice *vdev, uint32_t features)
 {
     VirtIONet *n = to_virtio_net(vdev);
@@ -580,6 +595,7 @@ PCIDevice *virtio_net_init(PCIBus *bus, NICInfo *nd, int devfn)
     n->vdev.set_config = virtio_net_set_config;
     n->vdev.get_features = virtio_net_get_features;
     n->vdev.set_features = virtio_net_set_features;
+    n->vdev.bad_features = virtio_net_bad_features;
     n->vdev.reset = virtio_net_reset;
     n->rx_vq = virtio_add_queue(&n->vdev, 256, virtio_net_handle_rx);
     n->tx_vq = virtio_add_queue(&n->vdev, 256, virtio_net_handle_tx);

hw/virtio.c

@@ -451,6 +451,13 @@ static void virtio_ioport_write(void *opaque, uint32_t addr, uint32_t val)
 
     switch (addr) {
     case VIRTIO_PCI_GUEST_FEATURES:
+	/* Guest does not negotiate properly?  We have to assume nothing. */
+	if (val & (1 << VIRTIO_F_BAD_FEATURE)) {
+	    if (vdev->bad_features)
+		val = vdev->bad_features(vdev);
+	    else
+		val = 0;
+	}
         if (vdev->set_features)
             vdev->set_features(vdev, val);
         vdev->features = val;
@@ -490,7 +497,7 @@ static uint32_t virtio_ioport_read(void *opaque, uint32_t addr)
     switch (addr) {
     case VIRTIO_PCI_HOST_FEATURES:
         ret = vdev->get_features(vdev);
-        ret |= (1 << VIRTIO_F_NOTIFY_ON_EMPTY);
+        ret |= (1 << VIRTIO_F_NOTIFY_ON_EMPTY) | (1 << VIRTIO_F_BAD_FEATURE);
         break;
     case VIRTIO_PCI_GUEST_FEATURES:
         ret = vdev->features;

hw/virtio.h

@@ -32,6 +32,8 @@
 /* We notify when the ring is completely used, even if the guest is supressing
  * callbacks */
 #define VIRTIO_F_NOTIFY_ON_EMPTY        24
+/* A guest should never accept this.  It implies negotiation is broken. */
+#define VIRTIO_F_BAD_FEATURE		30
 
 /* from Linux's linux/virtio_ring.h */
 
@@ -82,6 +84,7 @@ struct VirtIODevice
     size_t config_len;
     void *config;
     uint32_t (*get_features)(VirtIODevice *vdev);
+    uint32_t (*bad_features)(VirtIODevice *vdev);
     void (*set_features)(VirtIODevice *vdev, uint32_t val);
     void (*get_config)(VirtIODevice *vdev, uint8_t *config);
     void (*set_config)(VirtIODevice *vdev, const uint8_t *config);