From: "Michael S. Tsirkin" <mst@redhat•com>
To: Jason Wang <jasowang@redhat•com>
Cc: netdev@vger•kernel.org, davem@davemloft•net
Subject: Re: [PATCH for 3.4 2/2] macvtap: do not zerocopy if iov needs more pages than MAX_SKB_FRAGS
Date: Tue, 6 Aug 2013 13:04:51 +0300 [thread overview]
Message-ID: <20130806100451.GG11051@redhat.com> (raw)
In-Reply-To: <1375781359-5764-2-git-send-email-jasowang@redhat.com>
On Tue, Aug 06, 2013 at 05:29:19PM +0800, Jason Wang wrote:
> commit ece793fcfc417b3925844be88a6a6dc82ae8f7c6 upstream.
>
> We try to linearize part of the skb when the number of iov is greater than
> MAX_SKB_FRAGS. This is not enough since each single vector may occupy more than
> one pages, so zerocopy_sg_fromiovec() may still fail and may break the guest
> network.
>
> Solve this problem by calculate the pages needed for iov before trying to do
> zerocopy and switch to use copy instead of zerocopy if it needs more than
> MAX_SKB_FRAGS.
>
> This is done through introducing a new helper to count the pages for iov, and
> call uarg->callback() manually when switching from zerocopy to copy to notify
> vhost.
>
> We can do further optimization on top.
>
> This bug were introduced from b92946e2919134ebe2a4083e4302236295ea2a73
> (macvtap: zerocopy: validate vectors before building skb).
>
> Cc: Michael S. Tsirkin <mst@redhat•com>
> Signed-off-by: Jason Wang <jasowang@redhat•com>
> Signed-off-by: David S. Miller <davem@davemloft•net>
Acked-by: Michael S. Tsirkin <mst@redhat•com>
> ---
> drivers/net/macvtap.c | 62 +++++++++++++++++++++++++++++-------------------
> 1 files changed, 37 insertions(+), 25 deletions(-)
>
> diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c
> index 5151f06..77ce8b2 100644
> --- a/drivers/net/macvtap.c
> +++ b/drivers/net/macvtap.c
> @@ -642,6 +642,28 @@ static int macvtap_skb_to_vnet_hdr(const struct sk_buff *skb,
> return 0;
> }
>
> +static unsigned long iov_pages(const struct iovec *iv, int offset,
> + unsigned long nr_segs)
> +{
> + unsigned long seg, base;
> + int pages = 0, len, size;
> +
> + while (nr_segs && (offset >= iv->iov_len)) {
> + offset -= iv->iov_len;
> + ++iv;
> + --nr_segs;
> + }
> +
> + for (seg = 0; seg < nr_segs; seg++) {
> + base = (unsigned long)iv[seg].iov_base + offset;
> + len = iv[seg].iov_len - offset;
> + size = ((base & ~PAGE_MASK) + len + ~PAGE_MASK) >> PAGE_SHIFT;
> + pages += size;
> + offset = 0;
> + }
> +
> + return pages;
> +}
>
> /* Get packet from user space buffer */
> static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
> @@ -688,31 +710,15 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
> if (unlikely(count > UIO_MAXIOV))
> goto err;
>
> - if (m && m->msg_control && sock_flag(&q->sk, SOCK_ZEROCOPY))
> - zerocopy = true;
> -
> - if (zerocopy) {
> - /* Userspace may produce vectors with count greater than
> - * MAX_SKB_FRAGS, so we need to linearize parts of the skb
> - * to let the rest of data to be fit in the frags.
> - */
> - if (count > MAX_SKB_FRAGS) {
> - copylen = iov_length(iv, count - MAX_SKB_FRAGS);
> - if (copylen < vnet_hdr_len)
> - copylen = 0;
> - else
> - copylen -= vnet_hdr_len;
> - }
> - /* There are 256 bytes to be copied in skb, so there is enough
> - * room for skb expand head in case it is used.
> - * The rest buffer is mapped from userspace.
> - */
> - if (copylen < vnet_hdr.hdr_len)
> - copylen = vnet_hdr.hdr_len;
> - if (!copylen)
> - copylen = GOODCOPY_LEN;
> + if (m && m->msg_control && sock_flag(&q->sk, SOCK_ZEROCOPY)) {
> + copylen = vnet_hdr.hdr_len ? vnet_hdr.hdr_len : GOODCOPY_LEN;
> linear = copylen;
> - } else {
> + if (iov_pages(iv, vnet_hdr_len + copylen, count)
> + <= MAX_SKB_FRAGS)
> + zerocopy = true;
> + }
> +
> + if (!zerocopy) {
> copylen = len;
> linear = vnet_hdr.hdr_len;
> }
> @@ -724,9 +730,15 @@ static ssize_t macvtap_get_user(struct macvtap_queue *q, struct msghdr *m,
>
> if (zerocopy)
> err = zerocopy_sg_from_iovec(skb, iv, vnet_hdr_len, count);
> - else
> + else {
> err = skb_copy_datagram_from_iovec(skb, 0, iv, vnet_hdr_len,
> len);
> + if (!err && m && m->msg_control) {
> + struct ubuf_info *uarg = m->msg_control;
> + uarg->callback(uarg);
> + }
> + }
> +
> if (err)
> goto err_kfree;
>
> --
> 1.7.1
next prev parent reply other threads:[~2013-08-06 10:03 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-06 9:29 [PATCH for 3.4 1/2] vhost: zerocopy: poll vq in zerocopy callback Jason Wang
2013-08-06 9:29 ` [PATCH for 3.4 2/2] macvtap: do not zerocopy if iov needs more pages than MAX_SKB_FRAGS Jason Wang
2013-08-06 10:04 ` Michael S. Tsirkin [this message]
2013-08-06 10:04 ` [PATCH for 3.4 1/2] vhost: zerocopy: poll vq in zerocopy callback Michael S. Tsirkin
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