FreeBSD bhyve VM Exiting

[Neel Natu]

Hi Shawn,

On Fri, Dec 26, 2014 at 6:26 AM, Shawn Webb <lattera at gmail.com> wrote:
> Hey All,
>
> I'm running a FreeBSD/amd64 11-current (r276204) guest VM in bhyve. It
> seems that running Poudriere in it causes the VM to exit.
>
> This is what bhyve outputs when the VM dies:
>
>         reason          VMX
>         rip             0xffffffff80d68564
>         inst_length     5
>         status          0
>         exit_reason     2
>         qualification   0x0000000000000000
>         inst_type               0
>         inst_error              0
>
> I have no idea what "reason VMX" means or what "exit_reason 2" means. Is
> there a way to decode that?
>

Exit reason '2' is a triple fault.

> What kinds of info/data do you guys need to debug this?
>

You'll need a FreeBSD host with svn revision >= 276098 and a custom
kernel config to enable KTR.
https://svnweb.freebsd.org/base?view=revision&revision=276098

Then you can set the following tunable "hw.vmm.trace_guest_exceptions"
to "1" before loading vmm.ko. This will cause bhyve to trace all guest
exceptions via KTR. You can verify that the tunable took effect using
'sysctl hw.vmm.trace_guest_exceptions'.

When the bhyve process exits you can then dump the KTR entries using
something like this: 'sudo ktrdump -cto /tmp/ktrdump.out'. You'll
probably want to do this in a script so the ktrdump(8) happens
immediately after bhyve(8) exits.

I use the following options in my kernel config to enable KTR:
options KTR
options KTR_MASK=(KTR_GEN)
options KTR_ENTRIES=(4*1024*1024)

Hope this helps.

best
Neel

> Thanks,
>
> Shawn
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