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Date: Wed, 28 Oct 2015 09:08:25 +0200
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Andy Lutomirski <luto@...nel.org>
Cc: linux-kernel@...r.kernel.org, Joerg Roedel <jroedel@...e.de>,
Christian Borntraeger <borntraeger@...ibm.com>,
Cornelia Huck <cornelia.huck@...ibm.com>,
Sebastian Ott <sebott@...ux.vnet.ibm.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Christoph Hellwig <hch@....de>, benh@...nel.crashing.org,
KVM <kvm@...r.kernel.org>, dwmw2@...radead.org,
Martin Schwidefsky <schwidefsky@...ibm.com>,
linux-s390 <linux-s390@...r.kernel.org>,
virtualization@...ts.linux-foundation.org,
Andy Lutomirski <luto@...capital.net>
Subject: Re: [PATCH v3 1/3] virtio_net: Stop doing DMA from the stack
On Tue, Oct 27, 2015 at 11:38:58PM -0700, Andy Lutomirski wrote:
> From: Andy Lutomirski <luto@...capital.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: "Michael S. Tsirkin" <mst@...hat.com>
> Cc: virtualization@...ts.linux-foundation.org
> Reviewed-by: Joerg Roedel <jroedel@...e.de>
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
Same issues as v2 (I only saw v3 now).
I've proposed an alternative patch.
> ---
>
> 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?
>
> (This is unchanged from v2.)
>
> 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
--
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