Messages in this thread | | | Date | Wed, 17 Jul 2013 14:06:58 +0300 | From | "Michael S. Tsirkin" <> | Subject | Re: [PATCH net 2/2] macvtap: do not zerocopy if iov needs more pages than MAX_SKB_FRAGS |
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On Wed, Jul 17, 2013 at 06:32:11PM +0800, Jason Wang wrote: > 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> > --- > drivers/net/macvtap.c | 58 +++++++++++++++++++++++++++++++----------------- > 1 files changed, 37 insertions(+), 21 deletions(-) > > diff --git a/drivers/net/macvtap.c b/drivers/net/macvtap.c > index a7c5654..e200f11 100644 > --- a/drivers/net/macvtap.c > +++ b/drivers/net/macvtap.c > @@ -698,6 +698,28 @@ 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, > @@ -744,31 +766,19 @@ 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) { > + if (m && m->msg_control && sock_flag(&q->sk, SOCK_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. > */
We don't linearize parts to make them fit, we simply fall back to data copy. So this comment no longer applies, right?
> - 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; > + 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; > } > @@ -780,9 +790,15 @@ 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, false); > + } > + } > + > if (err) > goto err_kfree; > > -- > 1.7.1
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