On 18/12/13 21:02, John Baldwin wrote:
> On Saturday, December 14, 2013 3:15:45 am Roger Pau Monné wrote:
>> On 14/12/13 03:28, Neel Natu wrote:
>>> Hi John,
>>> On Fri, Dec 13, 2013 at 2:09 PM, John Baldwin <j...@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 <j...@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?
>> Can you use the hook in cpususpend_handler? It's cpu_ops.cpu_resume, and
>> gets called on each CPU before returning from the handler.
> That is the right place, yes.  However, I'm worried about collisions.  Can 
> you 
> run nested VMM's under Xen?  That is, can a xenhvm guest start a bhyve vmm?

In theory yes, but AFAIK nested virtualization support in Xen is not
really stable (it's still marked as experimental).

> If so, then you would need to run both cpu_resume handlers.  Also, cpu_resume 
> isn't run on the CPU that initiates the suspend.  For now I will stick with a
> dedicated vmm_resume_p hook, but we may want to revisit that at some point.

Using something like an event handler would be the best solution, but
that doesn't work on interrupt context due to the usage of mutexes.

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