xen-netback: Handle guests with too many frags

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Xen network protocol had implicit dependency on MAX_SKB_FRAGS. Netback has to
handle guests sending up to XEN_NETBK_LEGACY_SLOTS_MAX slots. To achieve that:
- create a new skb
- map the leftover slots to its frags (no linear buffer here!)
- chain it to the previous through skb_shinfo(skb)->frag_list
- map them
- copy and coalesce the frags into a brand new one and send it to the stack
- unmap the 2 old skb's pages

It's also introduces new stat counters, which help determine how often the guest
sends a packet with more than MAX_SKB_FRAGS frags.

NOTE: if bisect brought you here, you should apply the series up until
"xen-netback: Timeout packets in RX path", otherwise malicious guests can block
other guests by not releasing their sent packets.

Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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This commit is contained in:

Zoltan Kiss 2014-03-06 21:48:29 +00:00 • committed by David S. Miller

parent 1bb332af4c

commit e3377f36ca

3 changed files with 162 additions and 10 deletions

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1

drivers/net/xen-netback/common.h

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7

drivers/net/xen-netback/interface.c

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164

drivers/net/xen-netback/netback.c

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