guest suspend/resume & virtio: vring errors

[Michael Tokarev <mjt@tls.msk.ru>]

I tried suspend/resume cycle for a linux guest
today, with 100% failure result.  There are 2
possible scenarious after resume (you need
pretty recent guest kernel for it to work at
all, earlier kernels, incl. early 2.6.32, just
stops somewhere at the start of suspend cycle,
but 2.6.32.42 and 3.0-rc6 "works"), both are
in the same place but different viewpoint.

It is either guest complains

 virtio_net virtio0: input:id 2 is not a head!

and enters an endless loop eating 100% CPU, or
qemu-kvm exits (aborts) with the message:

 kvm: Guest moved used index from 1 to 0

this is when trying to use virtio-net.

The same happens when disabling network entirely:
it complains about virtio-blk in the same way,
for example

 kvm: Guest moved used index from 1 to 49285

qemu-kvm is of version 0.14.1 so far, I'll try
a git version later.

With e1000 instead of virtio-net-pci, the suspend
does not complete - guest kernel freezes after the
message "Suspending console(s)" and does not respond
(but does not eat 100% CPU either) - the same as for
older guest kernel.

Has anyone succeeded suspend/resume cycle?

Thanks!

/mjt