linux-kernel - Re: [PATCH v11] kvm: notify host when the guest is panicked

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Message-ID: <20121120213349.GA31355@amt.cnet>
Date:	Tue, 20 Nov 2012 19:33:49 -0200
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Hu Tao <hutao@...fujitsu.com>
Cc:	Sasha Levin <levinsasha928@...il.com>,
	Wen Congyang <wency@...fujitsu.com>,
	kvm list <kvm@...r.kernel.org>,
	qemu-devel <qemu-devel@...gnu.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Avi Kivity <avi@...hat.com>,
	"Daniel P. Berrange" <berrange@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	Gleb Natapov <gleb@...hat.com>,
	Blue Swirl <blauwirbel@...il.com>,
	Eric Blake <eblake@...hat.com>,
	Andrew Jones <drjones@...hat.com>,
	Luiz Capitulino <lcapitulino@...hat.com>
Subject: Re: [PATCH v11] kvm: notify host when the guest is panicked

On Tue, Nov 20, 2012 at 06:09:48PM +0800, Hu Tao wrote:
> Hi Marcelo,
> 
> On Tue, Nov 13, 2012 at 12:19:08AM -0200, Marcelo Tosatti wrote:
> > On Fri, Nov 09, 2012 at 03:17:39PM -0500, Sasha Levin wrote:
> > > On Mon, Nov 5, 2012 at 8:58 PM, Hu Tao <hutao@...fujitsu.com> wrote:
> > > > But in the case of panic notification, more dependency means more
> > > > chances of failure of panic notification. Say, if we use a virtio device
> > > > to do panic notification, then we will fail if: virtio itself has
> > > > problems, virtio for some reason can't be deployed(neither built-in or
> > > > as a module), or guest doesn't support virtio, etc.
> > > 
> > > Add polling to your virtio device. If it didn't notify of a panic but
> > > taking more than 20 sec to answer your poll request you can assume
> > > it's dead.
> > > 
> > > Actually, just use virtio-serial and something in userspace on the guest.
> > 
> > They want the guest to stop, so a memory dump can be taken by management
> > interface.
> > 
> > Hu Tao, lets assume port I/O is the preferred method for communication.
> 
> Okey.
> 
> > Now, the following comments have still not been addressed:
> > 
> > 1) Lifecycle of the stopped guest and interaction with other stopped
> > states in QEMU.
> 
> Patch 3 already deals with run state transitions. But in case I'm
> missing something, could you be more specific?

- What are the possibilities during migration? Say:
	- migration starts.
	- guest panics.
	- migration starts vm on other side?
- Guest stopped due to EIO.
	- guest vcpuN panics, VMEXIT but still outside QEMU.
	- QEMU EIO error, stop vm.
	- guest vcpuN completes, processes IO exit.
        - system_reset due to panic.
- Add all possibilities that should be verified (that is, interaction 
of this feature with other stopped states in QEMU).

---

- What happens if the guest has reboot-on-panic configured? Does it take
precedence over hypervisor notification?



Out of curiosity, does kexec support memory dumping?

> > 2) Format of the interface for other architectures (you can choose
> > a different KVM supported architecture and write an example).
> > 
> > 3) Clear/documented management interface for the feature.
> 
> It is documented in patch 0: Documentation/virtual/kvm/pv_event.txt.
> Does it need to be improved?

This is documentation for the host<->guest interface. There is no 
documentation on the interface for management.
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