RE: [Xen-devel] DomU panic in net_rx_action *initiated by another DomU*; 7503:20d1a79ebe31

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> Pardon me replying to my own post; it was only after hitting 
> "send" on the first one I took a closer look and found a much 
> more interesting (and worrisome) aspect to the issue I've 
> been seeing: Another DomU crashed with the same error at the 
> same time. This one was testing an experimental Linux kernel 
> patch (impacting procfs handling of symlinks), and 
> particularly unstable for that reason. It's interesting, 
> though, that the other DomU (without any such patch applied) 
> appeared to be impacted as well by the same issue.

I think this issue is at least approximately understood, and is present
in all xen x86_64 kernels:

rogue read-only mappings to linux heap pages left over from the 'initial
mapping' are preventing the netfront driver unmapping pages to hand over
as rx free buffers. This is compounded by the failure handling path
being slightly borked.

Ian

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