On 07/17/2013 07:06 PM, Michael S. Tsirkin wrote:
> 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 <[email protected]>
>> Signed-off-by: Jason Wang <[email protected]>
>> ---
>> 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?
Right, I forget to remove them. Will do it in V2.
>> - 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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