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Re: [Xen-users] [RESOLVED] Windows VM does not see NIC; "22 feature-rx-notify is mandatory" in dmesg

On Tue, 2015-02-03 at 11:30 -0500, Stephen Oberholtzer wrote:
> After installing 3.16.7-ckt4-2 from sid my NIC came back! Woohoo!
> Elias said "long story, ask Google" though I don't know what to ask
> Google. When I search for "feature-rx-notify mandatory", all I seem to
> get are patches making it mandatory, and complaints that it breaks
> stubdoms (which I am not using.)
> Could someone please explain what went down here?  This is what I've
> managed to piece together (mostly guesswork):
> * Some security hole was discovered when something was missing
> "feature-rx-notify".
> http://lists.xen.org/archives/html/xen-devel/2014-10/msg02698.html
> simply says "Frontends"; to me that would mean xl or possibly qemu,
> but apparently it's referring to something else.

It means the netfront driver in the guest, i.e. xen-netfront.ko in Linux
or whatever PVHVM driver you use in Windows.

> * Something changed in a recent Linux kernel update that tripped over
> this feature-rx-notify-is-mandatory patch, which prevented VIF devices
> from working in certain circumstances (including mine.)  I'm not sure
> what that could have been, though.

Not the Linux kernel, but your netfront driver (the PVHVM driver) turned
out not support feature-rx-notify, hence didn't work with the driver
updated as above. (IOW "I am not aware of any frontends that do not
implement this." turned out to be based on incomplete information).

stubdoms turned out to be another case of a netfront which didn't
implement feature-rx-notify which was noticed first.

> (This next one is a total guess.)
> * The PVHVM drivers installed on the VM included a network driver,
> that tried to replace the emulated NIC with a VIF.  However, due to
> the previous issue, the the VIF could not be brought up; however, the
> virtual NIC was removed anyway. (The PV driver probably ought to have
> generated an event log message for this.)



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