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

[Hu Tao]

On Sun, Mar 03, 2013 at 11:17:38AM +0200, Gleb Natapov wrote:
> 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

guest crash, lockup, or warning.[1] But the first purpose is to do panic
notification(panic event). Since at the point the guest is panicked, I
think it's better to keep the interface as simple as possible.

[1] http://wiki.qemu.org/Features/PVCrashDetection

> stop pretending that device is generic and make it do once thing but do

you mean make the interface just do panic notification?

> 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

Do we have to request the ID from some orgnazation?

> devices. After that you will be able to create device with _HID(QEMU0001)

QMU0001, I think. EISA ID requires it to have only 3 letters for PNP ID.

> 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.

Thanks for the information!

> 
> 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.