Recently Upgrade Virtualbox from 4.3 to 5.0 (linux host). mostly existing VM work well with default paravirtualized interface (such as KVM or Hyper-V).
A problematic VM I noticed is Windows 7 32bit (in fact WindowsThinPC). Just share some progress while I try to solve it.
This VM's main rule is a RDP server. Sometimes I run firefox remotely on it. but VM crash lots after I upgrade Virtualbox to 5.0. It crash VM (and break RDP connection) when I try to browse certain website. Virtualbox 5.0 log showing heartbeat lost, only thing could do was RESET guest.
I suspect Hyper-V (paravirtualized interface) at first, but problem still there without this setting.
Later I disable PAE/NX, looks more stable now.
This is not conclusion, I will post more if any change.
(Update 1) 10 minutes add:
Looks problem still exist!
PAE/NX OFF help a little but Guest still crash for no reason....
(Update 2)1 hour add:
It's still not clear reason why VM crash...
and VM crash happened when I browse website with firefox.So, maybe firefox is troublemaker? I dunno, it's hard to detect.
test with fx 31 and fx 38, results are similar, they crash sometimes.
(Reference to another XP guest on same host, it run firefox without problem...)
Next move is downgrade to virtualbox 4.3 in next few day...
(Update 3)
Turn out it's not virtualbox 5.0.0 's fault, It can reproduce with version 4.3.28.
and not cause by PAE/NX, Nested Paging or VT-x ...
(Update 4)
Later, I noticed VM's firewall activity. I lost VM's control when network connections over 500+. So I realize this is guest's network problem, not caused by firefox or virtualbox.
I installed alternative network driver for guest OS, and solved the problem.
This VM's networking is set to bridged networking, virtual NIC is virtio-net.
I upgrade Virtualbox 5.0.0 a couple days before. after that day I also upgrade virtio-net drivers from Fedora.( http://fedorapeople.org/groups/virt/virtio-win/direct-downloads/ )
I chose an unstable version 0.1.105 to apply on Guest OS(it turns out a bad move). Now I backward to version 0.1.100 and virtio-net no longer crash Guest OS=Windows 7 32bit.
CONCLUSION
Beware newest drivers.
