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

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Message-ID: <20121121093928.GN21208@redhat.com>
Date:	Wed, 21 Nov 2012 11:39:28 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>
Cc:	Hu Tao <hutao@...fujitsu.com>,
	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>,
	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 07:33:49PM -0200, Marcelo Tosatti wrote:
> 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).
> 
BTW I do remember getting asserts while using breakpoints via gdbstub
and stop/cont from the monitor.

> ---
> 
> - 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.

--
			Gleb.
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