[PATCH v2 1/3] virtio_net: Stop doing DMA from the stack
From: Andy Lutomirski <luto@kernel.org>
Date: 2015-10-28 05:31:03
From: Andy Lutomirski <luto@amacapital.net> 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. Cc: netdev@vger.kernel.org Cc: "Michael S. Tsirkin" <mst@redhat.com> Cc: virtualization@lists.linux-foundation.org Reviewed-by: Joerg Roedel <redacted> Signed-off-by: Andy Lutomirski <luto@kernel.org> --- Hi Michael and DaveM- This is a prerequisite for the virtio DMA fixing project. It works as a standalone patch, though. Would it make sense to apply it to an appropriate networking tree now? drivers/net/virtio_net.c | 53 ++++++++++++++++++++++++++++++++---------------- 1 file changed, 36 insertions(+), 17 deletions(-)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index d8838dedb7a4..4f10f8a58811 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c@@ -976,31 +976,43 @@ 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; + + struct { + struct virtio_net_ctrl_hdr ctrl; + virtio_net_ctrl_ack status; + } *buf; + unsigned out_num = 0, tmp; + bool ret; /* Caller should know better */ BUG_ON(!virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_VQ)); - ctrl.class = class; - ctrl.cmd = cmd; + buf = kmalloc(sizeof(*buf), GFP_ATOMIC); + if (!buf) + return false; + buf->status = ~0; + + buf->ctrl.class = class; + buf->ctrl.cmd = cmd; /* Add header */ - sg_init_one(&hdr, &ctrl, sizeof(ctrl)); + sg_init_one(&hdr, &buf->ctrl, sizeof(buf->ctrl)); sgs[out_num++] = &hdr; if (out) sgs[out_num++] = out; /* Add return status. */ - sg_init_one(&stat, &status, sizeof(status)); + sg_init_one(&stat, &buf->status, sizeof(buf->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; + if (unlikely(!virtqueue_kick(vi->cvq))) { + ret = (buf->status == VIRTIO_NET_OK); + goto out; + } /* Spin for a response, the kick causes an ioport write, trapping * into the hypervisor, so the request should be handled immediately.
@@ -1009,7 +1021,11 @@ 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; + ret = (buf->status == VIRTIO_NET_OK); + +out: + kfree(buf); + return ret; } static int virtnet_set_mac_address(struct net_device *dev, void *p)
@@ -1151,7 +1167,7 @@ static void virtnet_set_rx_mode(struct net_device *dev) { struct virtnet_info *vi = netdev_priv(dev); struct scatterlist sg[2]; - u8 promisc, allmulti; + u8 *cmdbyte; struct virtio_net_ctrl_mac *mac_data; struct netdev_hw_addr *ha; int uc_count;
@@ -1163,22 +1179,25 @@ 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); + cmdbyte = kmalloc(sizeof(*cmdbyte), GFP_ATOMIC); + if (!cmdbyte) + return; - sg_init_one(sg, &promisc, sizeof(promisc)); + sg_init_one(sg, cmdbyte, sizeof(*cmdbyte)); + *cmdbyte = ((dev->flags & IFF_PROMISC) != 0); 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"); - - sg_init_one(sg, &allmulti, sizeof(allmulti)); + *cmdbyte ? "en" : "dis"); + *cmdbyte = ((dev->flags & IFF_ALLMULTI) != 0); 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"); + *cmdbyte ? "en" : "dis"); + + kfree(cmdbyte); uc_count = netdev_uc_count(dev); mc_count = netdev_mc_count(dev);
--
2.4.3