Re: [Xen-devel] Early ACPI events prevent subsequent ACPI functionality on xen 4.3 + HVM domU

[George Dunlap <George.Dunlap@xxxxxxxxxxxxx>]

On Tue, May 21, 2013 at 2:39 PM, George Dunlap
<George.Dunlap@xxxxxxxxxxxxx> wrote:
> On Sat, May 18, 2013 at 10:55 AM, Alex Bligh <alex@xxxxxxxxxxx> wrote:
>> Ian,
>>
>>
>> --On 17 May 2013 18:35:51 +0100 Ian Campbell <ian.campbell@xxxxxxxxxx>
>> wrote:
>>
>>>> We are using Xen-4.3-rc1 with dom0 running Ubuntu Precise and
>>>> 3.5.0-23-generic kernel, and domU running Ubuntu Precise (12.04) cloud
>>>> images running 3.2.0-39-virtual. We are using the xl.conf below on
>>>> qemu-upstream-dm and HVM and two identical sending and receiving
>>>> machines (hardware and software)
>>>>
>>>> If a dom-U HVM server is started with ACPI enabled, and an ACPI event
>>>> (such as shutdown or reboot) is sent to domU before the BIOS and/or
>>>> operating system in the dom-U has initialised ACPI, then all
>>>> subsequent ACPI events are ignored.
>>>
>>>
>>> I suppose something must be getting latched and since no one was around
>>> at the time to clear it no further events are possible. Not sure if this
>>> is a qemu or a guest issue though.
>>
>>
>> I can confirm it does not happen with KVM with the same guest, and it
>> happens with multiple Linux guests on Xen. Our test suite triggers it
>> every time.
>>
>> It's a pain because if someone starts a server by accident and immediately
>> goes to shut it down, they have to do an ungraceful destroy rather than
>> a clean shutdown.
>
> So this appears to be an xl toolstack thing.  I managed to reproduce
> your results using "xl shutdown -F [domain]"; but if you then do "xl
> trigger [domian] power", the domain shuts down as normal.
>
> That at least should give you a work-around so you don't have to do
> "xl destroy".
>
> I'll take a look and see if I can figure out what's going on...

Actually, this has nothing to do with ACPI at all.

"xl shutdown" will *always* attempt to issue a PV shutdown command
first.  If it thinks there is no PV drivers present, *and* the '-F'
option is added, then it will also attempt to send an acpi power
event.

So a plain "xl shutdown" maps to:
if( pv_drivers_available(domain) )
  write_xenstore_node();

The PV drivers in domU should have watches on the xenstore node
written to cause the shutdown.  But apparently there's a window
between the time pv_drivers_available() returns succeeds and the time
this watch is set up; and if the node is written between these two
times, then the notification gets dropped.

xl seems to use HVM_PARAM_CALLBACK_IRQ being non-zero as an indicator.

Dave and Paul, does this race exist in XenServer with the Citrix PV
drivers?  How does xe detect whether pv drivers are available for an
HVM domain? And will the Citrix PV drivers check for the existence of
shutdown commands before they start a watch?

 -George

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