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| /freebsd/sys/dev/xen/netfront/ |
| H A D | netfront.c | diff dabb3db7a817f003af3f89c965ba369c67fc4910 Thu Nov 03 13:29:22 CET 2022 Roger Pau Monné <royger@FreeBSD.org> xen/netfront: deal with mbuf data crossing a page boundary
There's been a report recently of mbufs with data that crosses a page
boundary. It seems those mbufs are generated by the iSCSI target
system:
https://lists.xenproject.org/archives/html/xen-devel/2021-12/msg01581.html
In order to handle those mbufs correctly on netfront use the bus_dma
interface and explicitly request that segments must not cross a page
boundary. No other requirements are necessary, so it's expected that
bus_dma won't need to bounce the data and hence it shouldn't
introduce a too big performance penalty.
Using bus_dma requires some changes to netfront, mainly in order to
accommodate for the fact that now ring slots no longer have a 1:1
match with mbufs, as a single mbuf can use two ring slots if the data
buffer crosses a page boundary. Store the first packet of the mbuf
chain in every ring slot that's used, and use a mbuf tag in order to
store the bus_dma related structures and a refcount to keep track of
the pending slots before the mbuf chain can be freed.
Reported by: G.R.
Tested by: G.R.
MFC: 1 week
Differential revision: https://reviews.freebsd.org/D33876
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