Re: [Qemu-devel] [PATCH v14 3/4] introduce pvevent device to deal with panicked event

[Gleb Natapov <gleb@redhat.com>]

On Thu, Mar 14, 2013 at 12:23:01PM +0100, Alexander Graf wrote:
> 
> On 14.03.2013, at 12:03, Paolo Bonzini wrote:
> 
> > Il 14/03/2013 12:00, Alexander Graf ha scritto:
> >> 
> >> On 14.03.2013, at 10:43, Paolo Bonzini wrote:
> >> 
> >>> Il 14/03/2013 10:19, Gleb Natapov ha scritto:
> >>>> On Thu, Mar 14, 2013 at 10:14:12AM +0100, Paolo Bonzini wrote:
> >>>>> Il 14/03/2013 09:15, Hu Tao ha scritto:
> >>>>>> pvevent device is used to send guest panic event from guest to qemu.
> >>>>>> 
> >>>>>> When guest panic happens, pvevent device driver will write a event
> >>>>>> number to IO port 0x505(which is the IO port occupied by pvevent device,
> >>>>>> by default). On receiving the event, pvevent device will pause guest
> >>>>>> cpu(s), and send a qmp event QEVENT_GUEST_PANICKED.  
> >>>>>> 
> >>>>>> TODO: make the IO port configurable
> >>>>> 
> >>>>> The port is already configurable as far as the device is concerned; when
> >>>>> you add the port to the PC boards you will have to wind up fw-cfg.
> >>>> 
> >>>> Why not add fw-cfg when device is created (with -device for instance)?
> >>> 
> >>> It depends on what we decide is the supported interface for the device:
> >>> 
> >>> * it can be an ISA device; the interface is the I/O port and ACPI
> >> 
> >> Is there any particular reason it's an ISA device with a PIO port,
> >> rather than a platform / sysbus device with MMIO access? With the
> >> latter, we could easily reuse the device on other platforms (ppc, arm)
> >> and even the guest driver code for platforms that do ACPI (arm?).
> > 
> > Where would you place the MMIO area on x86?  
> 
> Wherever the board thinks it makes sense.
> 
On x86 it makes sense to put it in IO space :)

> > But anyway you can easily
> > define an MMIO variant, the guest driver code will be shared (the ACPI
> > in the firmware no, of course).
> 
> Yes, at which point we have 2 variants where we could have had 1. I don't know if it's worth caring about it, just wanted to bring it up.
> 
We can have the same device and control via properties what address
space to use for the device.

> > 
> >> Also, don't the Xen guys already have a similar interface? Could we at least share the guest side implementation maybe?
> > 
> > I think Xen uses xenstore for this, or a hypercall I don't remember.
> > But not something that can be shared unfortunately.
> 
> At least the guest kernel hook could be shared. In fact, how does that one work with this device? I've only seen an ACPI patch so far. Does ACPI already support panic hooks?
> 
> 
No need for any special hook to use the device. There was a separate
patch with guest platform driver that uses the device. IN fact it should
work on XEN too.

--
			Gleb.