Panic starting a bhyve guest after resume

[Neel Natu]

Hi John,

On Fri, Dec 13, 2013 at 2:09 PM, John Baldwin <jhb at freebsd.org> wrote:
> On Thursday, December 12, 2013 4:00:08 pm Neel Natu wrote:
>> Hi John,
>>
>> On Thu, Dec 12, 2013 at 12:11 PM, John Baldwin <jhb at freebsd.org> wrote:
>> > If I suspend and resume my laptop and then try to start a guest after the
>> > resume, I get an odd panic.  It generates a privileged instruction fault (in
>> > kernel mode) for 'vmclear'.  I've checked CR4 and it claims that VMXE is set.
>> > I dont have any other ideas off the top of my head on what I should be poking
>> > at?  It looks like we read a bunch of MSRs in vmx_init(), but we don't write
>> > to them, and all vmx_enable() does on each CPU is set VMXE in CR4 from what I
>> > can tell.
>> >
>>
>> It also does a "vmxon" on each logical cpu which may also need to be
>> done after a resume.
>
> Ah, yes it does.  That was sufficient both for starting a new guest after
> resume and even doing a suspend/resume while a guest was active (and the
> guest continued to run fine).  I have a hacky patch for this.  One, it
> includes both a suspend and resume hook for VMM, though for my testing I only
> needed a resume hook to invoke vmxon.  Second, the name of vmx_resume2()
> is a total hack (because vmx_resume() was already taken.  I think for now
> if I were to commit this, I'd just add the resme hook and maybe call the
> Intel method vmx_reset() or vmx_restore()?
>
> http://people.freebsd.org/~jhb/patches/bhyve_resume.patch
>

There seems to be a race after the APs are restarted and before
'vmm_resume_p()' where it would be problematic to execute a VMX
instruction.

Perhaps we should enable VMX on each cpu before they return to the
interrupted code?

best
Neel

> --
> John Baldwin