Roger Pau Monné dabb3db7a8 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		2022-11-03 13:32:21 +01:00
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netfront.c	xen/netfront: deal with mbuf data crossing a page boundary	2022-11-03 13:32:21 +01:00