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Re: [Xen-devel] Nested virtualization instabilities
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On 16/12/2013 11:05, Etzion Bar-Noy
wrote:
Hi.
I am using the unstable
build-from-source of Xen
community. It reports as 4.4,
and was pulled from Git few
days ago. The problem I will
describe below appears on
version 4.3.1, compiled from
source as well. In both cases
- I used spec file to create
my own RPMs, because it's the
right method of doing it.
Problem: When VM running under
HVM which is a hypervisor
(XenServer 6.2 or VMware
ESXi5.5) attempts to start a
(HVM) virtual machine, the
following happens, 100%
reproducible on this server.
XenServer: domain crash. XenServer
restarts itself. It doesn't happen
for PV on XenServer VM
VMware: An "unknown failure", which
leads me to think that the nested
virtualization properties are not
forwarded correctly to DomU
<snip>
(XEN) <vm_launch_fail> error code 7
(XEN) domain_crash_sync called from vmcs.c:1293
(XEN) Domain 8 (vcpu#0) crashed on cpu#4:
(XEN) ----[ Xen-4.4-unstable x86_64 debug=y
Not tainted ]----
(XEN) CPU: 4
(XEN) RIP: 0000:[<0000000000000000>]
(XEN) RFLAGS: 0000000000000002 CONTEXT: hvm
guest
(XEN) rax: 0000000000000000 rbx:
ffff830824f98000 rcx: ffff830824f9ff80
(XEN) rdx: ffff82d0801d0cf9 rsi:
0000000000000000 rdi: ffff82d0801de7fc
(XEN) rbp: ffff82d080105ab1 rsp:
0000000000000000 r8: 0000000000000004
(XEN) r9: ffff82d080105b20 r10:
ffff830824f9ff70 r11: 0000000000000000
(XEN) r12: ffff830824f9ff50 r13:
ffff830654f9e000 r14: ffff830824f9ff30
(XEN) r15: ffff82d080187e43 cr0:
0000000000000039 cr4: 0000000000002050
(XEN) cr3: 00000000feffa000 cr2:
0000000000000000
(XEN) ds: 0000 es: 0000 fs: 0000 gs:
0000 ss: 0000 cs: 0000
This is the problem.
Error code 7 is defined as "VM entry with invalid control field(s)"
At a guess, I would think that the L1 hypervisor is probing the
control fields (as that seems to be the only way of detecting
whether a feature is available or not), and this error might need
bouncing back to the VM.
Otherwise, the L1 hypervisor has decided it can use a particular
control, and Xen has insufficient validation if the L1 state.
Either way, it would be useful to know if there is a way for the
hardware to identify which control field it has an issue with...
~Andrew
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