Re: [PATCH v13 0/8] pv event interface between host and guest

From: Gleb Natapov <gleb@redhat.com>
To: Hu Tao <hutao@cn.fujitsu.com>
Cc: kvm list <kvm@vger.kernel.org>,
	qemu-devel <qemu-devel@nongnu.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"Daniel P. Berrange" <berrange@redhat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
	Jan Kiszka <jan.kiszka@siemens.com>,
	Blue Swirl <blauwirbel@gmail.com>, Eric Blake <eblake@redhat.com>,
	Andrew Jones <drjones@redhat.com>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	Sasha Levin <levinsasha928@gmail.com>,
	Luiz Capitulino <lcapitulino@redhat.com>,
	Anthony Liguori <aliguori@us.ibm.com>,
	Markus Armbruster <armbru@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Stefan Hajnoczi <stefanha@redhat.com>,
	Juan Quintela <quintela@redhat.com>,
	Orit Wasserman <owasserm@redhat.com>,
	Kevin Wolf <kwolf@redhat.com>,
	Wen Congyang <wency@cn.fujitsu.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Alexander Graf <agraf@suse.de>,
	Alex Williamson <alex.williamson@redhat.com>,
	Peter Maydell <peter.maydell@linaro.org>
Subject: Re: [PATCH v13 0/8] pv event interface between host and guest
Date: Sun, 3 Mar 2013 11:17:38 +0200	[thread overview]
Message-ID: <20130303091738.GB23616@redhat.com> (raw)
In-Reply-To: <cover.1362051581.git.hutao@cn.fujitsu.com>

On Thu, Feb 28, 2013 at 08:13:10PM +0800, Hu Tao wrote:
> This series implements a new interface, kvm pv event, to notify host when
> some events happen in guest. Right now there is one supported event: guest
> panic.
> 
What other event do you have in mind? Is interface generic enough to
accommodate future, yet unknown, events. It allows to pass only one
integer specifying even type, what if additional info is needed? My be
stop pretending that device is generic and make it do once thing but do
it well? For generic even passing interface (whatever it may be needed
for) much more powerful virtio should be used.

On implementation itself I do not understand why is this kvm specific.
The only thing that makes it so is that you hook device initialization
into guest kvm initialization code, but this is obviously incorrect.
What stops QEMU tcg or Xen from reusing the same device for the same
purpose except the artificial limitation in a guest.

Reading data from a random ioports is not how you discover platform
devices in 21 century (and the data you read from unassigned port is not
guarantied to be zero, it may depend on QEMU version), you use ACPI for
that and Marcelo already pointed that to you. Having little knowledge of
ACPI (we all do) is not a good reason to not doing it. We probably need
to reserve QEMU specific ACPI Plug and Play hardware ID to define our own
devices. After that you will be able to create device with _HID(QEMU0001)
in DSDT that supplies address information (ioport to use) and capability
supported. Guest uses acpi_get_devices() to discover a platform device by
its name (QEMU0001).  Then you put the driver for the platform device
into drivers/platform/x86/ and QEMU/kvm/Xen all will be able to use it.

On QEMU side of things I cannot comment much on how QOMified the device
is (it should be), I hope other reviews will verify it, but I noticed
that device is only initialized for PIIX, what about Q35?

--
			Gleb.