Message-ID: <20120814205339.GA14172@amt.cnet>
Date:	Tue, 14 Aug 2012 17:53:39 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Anthony Liguori <anthony@...emonkey.ws>,
	Wen Congyang <wency@...fujitsu.com>
Cc:	Yan Vugenfirer <yvugenfi@...hat.com>,
	kvm list <kvm@...r.kernel.org>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Gleb Natapov <gleb@...hat.com>,
	qemu-devel <qemu-devel@...gnu.org>, Avi Kivity <avi@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [Qemu-devel] [PATCH v8] kvm: notify host when the guest is
 panicked

On Tue, Aug 14, 2012 at 02:35:34PM -0500, Anthony Liguori wrote:
> Marcelo Tosatti <mtosatti@...hat.com> writes:
> 
> > On Tue, Aug 14, 2012 at 01:53:01PM -0500, Anthony Liguori wrote:
> >> Marcelo Tosatti <mtosatti@...hat.com> writes:
> >> 
> >> > On Tue, Aug 14, 2012 at 05:55:54PM +0300, Yan Vugenfirer wrote:
> >> >> 
> >> >> On Aug 14, 2012, at 1:42 PM, Jan Kiszka wrote:
> >> >> 
> >> >> > On 2012-08-14 10:56, Daniel P. Berrange wrote:
> >> >> >> On Mon, Aug 13, 2012 at 03:21:32PM -0300, Marcelo Tosatti wrote:
> >> >> >>> On Wed, Aug 08, 2012 at 10:43:01AM +0800, Wen Congyang wrote:
> >> >> >>>> We can know the guest is panicked when the guest runs on xen.
> >> >> >>>> But we do not have such feature on kvm.
> >> >> >>>> 
> >> >> >>>> Another purpose of this feature is: management app(for example:
> >> >> >>>> libvirt) can do auto dump when the guest is panicked. If management
> >> >> >>>> app does not do auto dump, the guest's user can do dump by hand if
> >> >> >>>> he sees the guest is panicked.
> >> >> >>>> 
> >> >> >>>> We have three solutions to implement this feature:
> >> >> >>>> 1. use vmcall
> >> >> >>>> 2. use I/O port
> >> >> >>>> 3. use virtio-serial.
> >> >> >>>> 
> >> >> >>>> We have decided to avoid touching hypervisor. The reason why I choose
> >> >> >>>> choose the I/O port is:
> >> >> >>>> 1. it is easier to implememt
> >> >> >>>> 2. it does not depend any virtual device
> >> >> >>>> 3. it can work when starting the kernel
> >> >> >>> 
> >> >> >>> How about searching for the "Kernel panic - not syncing" string 
> >> >> >>> in the guests serial output? Say libvirtd could take an action upon
> >> >> >>> that?
> >> >> >> 
> >> >> >> No, this is not satisfactory. It depends on the guest OS being
> >> >> >> configured to use the serial port for console output which we
> >> >> >> cannot mandate, since it may well be required for other purposes.
> >> >> > 
> >> >> Please don't forget Windows guests, there is no console and no "Kernel Panic" string ;)
> >> >> 
> >> >> What I used for debugging purposes on Windows guest is to register a bugcheck callback in virtio-net driver and write 1 to VIRTIO_PCI_ISR register.
> >> >> 
> >> >> Yan. 
> >> >
> >> > Considering whether a "panic-device" should cover other OSes is also \
> >
> >> > something to consider. Even for Linux, is "panic" the only case which
> >> > should be reported via the mechanism? What about oopses without panic? 
> >> >
> >> > Is the mechanism general enough for supporting new events, etc.
> >> 
> >> Hi,
> >> 
> >> I think this discussion is gone of the deep end.
> >> 
> >> Forget about !x86 platforms.  They have their own way to do this sort of
> >> thing.  
> >
> > The panic function in kernel/panic.c has the following options, which
> > appear to be arch independent, on panic:
> >
> > - reboot 
> > - blink
> 
> Not sure the semantics of blink but that might be a good place for a
> pvops hook.
> 
> >
> > None are paravirtual interfaces however.
> >
> >> Think of this feature like a status LED on a motherboard.  These
> >> are very common and usually controlled by IO ports.
> >> 
> >> We're simply reserving a "status LED" for the guest to indicate that it
> >> has paniced.  Let's not over engineer this.
> >
> > My concern is that you end up with state that is dependant on x86.
> >
> > Subject: [PATCH v8 3/6] add a new runstate: RUN_STATE_GUEST_PANICKED
> >
> > Having the ability to stop/restart the guest (and even introducing a 
> > new VM runstate) is more than a status LED analogy.
> 
> I must admit, I don't know why a new runstate is necessary/useful.  The
> kernel shouldn't have to care about the difference between a halted guest
> and a panicked guest.  That level of information belongs in userspace IMHO.
> 
> > Can this new infrastructure be used by other architectures?
> 
> I guess I don't understand why the kernel side of this isn't anything
> more than a paravirt op hook that does a single outb() with the
> remaining logic handled 100% in QEMU.

>From the patch description:

"Another purpose of this feature is: management app(for example:
libvirt) can do auto dump when the guest is panicked. If management
app does not do auto dump, the guest's user can do dump by hand if
he sees the guest is panicked."

Wen, auto dump means dump of guest memory?

In that case, the notification should obviously stop the guest 
otherwise the guest might be reset by the time memdump from QEMU 
monitor runs.

But kexec supports dumping of memory already (i suppose it can 
do automatic dump+{reboot,shutdown}).

> > Do you consider allowing support for Windows as overengineering?
> 
> I don't think there is a way to hook BSOD on Windows so attempting to
> engineer something that works with Windows seems odd, no?

Unsure about hooking at BSOD time. But Windows has configurable 
memory dump/reset/reboot, so yes it should not necessary.

> 
> Regards,
> 
> Anthony Liguori
> 
> >
> >> Regards,
> >> 
> >> Anthony Liguori
> >> 
> >> >
> >> >> 
> >> >> > Well, we have more than a single serial port, even when leaving
> >> >> > virtio-serial aside...
> >> >> > 
> >> >> > Jan
> >> >> > 
> >> >> > -- 
> >> >> > Siemens AG, Corporate Technology, CT RTC ITP SDP-DE
> >> >> > Corporate Competence Center Embedded Linux
> >> >> > --
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