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Re: [Xen-devel] [3.15-rc3] Bisected: xen-netback mangles packets between two guests on a bridge since merge of "TX grant mapping with SKBTX_DEV_ZEROCOPY instead of copy" series.

Let's see what that does different and if that gives an insight in what is going

The debug patch that i used is attached.
Here is some of the output, skb->data_len size sometimes varies slightly as does 
skb->truesize (is that allowed to become > 64k ?).
Yes, truesize can be over 64K, as it includes the aligned size of the data itself (64k max), struct skbuff and struct shared_info. However my calculation for the truesize might be wrong: I count all the frags as full sized pages (skb->truesize += i * PAGE_SIZE), but the last page is not necessarily used entirely by that frag. I had the idea that truesize should include the size of the whole page as we reserved it with alloc_page for this skb, but it might not be true. Btw. with you "skb->truesize -= nskb->data_len;" version truesize should end up around 128k, something entirely wrong. Can you try with "skb->truesize -= nskb->data_len;" in that line?
My repro env is underway in the meantime ...



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