On Wed, 2011-05-18 at 10:00 -0700, Shirley Ma wrote:

On Wed, 2011-05-18 at 19:51 +0300, Michael S. Tsirkin wrote:

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Yes, I agree.  I think for tcpdump, we really need to copy the

data

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anyway, to avoid guest changing it in between.  So we do that

and

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then

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use the copy everywhere, release the old one. Hmm? 

Yes. Old one use zerocopy, new one use copy data.

Thanks
Shirley

No, that's wrong, as they might become different with a
malicious guest. As long as we copied already, lets realease
the data and have everyone use the copy. 

Ok, I will patch pskb_expand_head to test it out. 

I am patching skb_copy, skb_clone, pskb_copy, pskb_expand_head to
convert a zero-copy skb to a copy skb to avoid this kind of issue.

This overhead won't impact macvtap/vhost TX zero-copy normally.

Shirley