virtio-net: Stop doing DMA from the stack

Once virtio starts using the DMA API, we won't be able to safely DMA
from the stack.  virtio-net does a couple of config DMA requests
from small stack buffers -- switch to using dynamically-allocated
memory.

This should have no effect on any performance-critical code paths.

Reported-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Andy Lutomirski <luto@kernel.org>

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index d8838de..f94ab78 100644 (file)
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -140,6 +140,12 @@ struct virtnet_info {
 
        /* CPU hot plug notifier */
        struct notifier_block nb;
+
+       /* Control VQ buffers: protected by the rtnl lock */
+       struct virtio_net_ctrl_hdr ctrl_hdr;
+       virtio_net_ctrl_ack ctrl_status;
+       u8 ctrl_promisc;
+       u8 ctrl_allmulti;
 };
 
 struct padded_vnet_hdr {
@@ -976,31 +982,30 @@ static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
                                 struct scatterlist *out)
 {
        struct scatterlist *sgs[4], hdr, stat;
-       struct virtio_net_ctrl_hdr ctrl;
-       virtio_net_ctrl_ack status = ~0;
        unsigned out_num = 0, tmp;
 
        /* Caller should know better */
        BUG_ON(!virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_VQ));
 
-       ctrl.class = class;
-       ctrl.cmd = cmd;
+       vi->ctrl_status = ~0;
+       vi->ctrl_hdr.class = class;
+       vi->ctrl_hdr.cmd = cmd;
        /* Add header */
-       sg_init_one(&hdr, &ctrl, sizeof(ctrl));
+       sg_init_one(&hdr, &vi->ctrl_hdr, sizeof(vi->ctrl_hdr));
        sgs[out_num++] = &hdr;
 
        if (out)
                sgs[out_num++] = out;
 
        /* Add return status. */
-       sg_init_one(&stat, &status, sizeof(status));
+       sg_init_one(&stat, &vi->ctrl_status, sizeof(vi->ctrl_status));
        sgs[out_num] = &stat;
 
        BUG_ON(out_num + 1 > ARRAY_SIZE(sgs));
        virtqueue_add_sgs(vi->cvq, sgs, out_num, 1, vi, GFP_ATOMIC);
 
        if (unlikely(!virtqueue_kick(vi->cvq)))
-               return status == VIRTIO_NET_OK;
+               return vi->ctrl_status == VIRTIO_NET_OK;
 
        /* Spin for a response, the kick causes an ioport write, trapping
         * into the hypervisor, so the request should be handled immediately.
@@ -1009,7 +1014,7 @@ static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
               !virtqueue_is_broken(vi->cvq))
                cpu_relax();
 
-       return status == VIRTIO_NET_OK;
+       return vi->ctrl_status == VIRTIO_NET_OK;
 }
 
 static int virtnet_set_mac_address(struct net_device *dev, void *p)
@@ -1151,7 +1156,6 @@ static void virtnet_set_rx_mode(struct net_device *dev)
 {
        struct virtnet_info *vi = netdev_priv(dev);
        struct scatterlist sg[2];
-       u8 promisc, allmulti;
        struct virtio_net_ctrl_mac *mac_data;
        struct netdev_hw_addr *ha;
        int uc_count;
@@ -1163,22 +1167,22 @@ static void virtnet_set_rx_mode(struct net_device *dev)
        if (!virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_RX))
                return;
 
-       promisc = ((dev->flags & IFF_PROMISC) != 0);
-       allmulti = ((dev->flags & IFF_ALLMULTI) != 0);
+       vi->ctrl_promisc = ((dev->flags & IFF_PROMISC) != 0);
+       vi->ctrl_allmulti = ((dev->flags & IFF_ALLMULTI) != 0);
 
-       sg_init_one(sg, &promisc, sizeof(promisc));
+       sg_init_one(sg, &vi->ctrl_promisc, sizeof(vi->ctrl_promisc));
 
        if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_RX,
                                  VIRTIO_NET_CTRL_RX_PROMISC, sg))
                dev_warn(&dev->dev, "Failed to %sable promisc mode.\n",
-                        promisc ? "en" : "dis");
+                        vi->ctrl_promisc ? "en" : "dis");
 
-       sg_init_one(sg, &allmulti, sizeof(allmulti));
+       sg_init_one(sg, &vi->ctrl_allmulti, sizeof(vi->ctrl_allmulti));
 
        if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_RX,
                                  VIRTIO_NET_CTRL_RX_ALLMULTI, sg))
                dev_warn(&dev->dev, "Failed to %sable allmulti mode.\n",
-                        allmulti ? "en" : "dis");
+                        vi->ctrl_allmulti ? "en" : "dis");
 
        uc_count = netdev_uc_count(dev);
        mc_count = netdev_mc_count(dev);