FW: RE: DOR : Example for injecting the interrupt to the guest

FW: RE: DOR : Example for injecting the interrupt to the guest

[Ajith Chandran]

Hello Dor,

Thank you so much for the quick reply. 

My project is to run a qnx4.4 legacy application (which talks to custom made hardware) on virtualized environment. I am using KVM for that and am able to read and write to the actual hardware. I used serial driver in qemu as a reference to develop my custom virtual driver. Let me know what specific details you want to know.

I know fairly well to trap the interrupt in the host side (linux). What I would require is some example on how to modify the qemu part of the code, so that it the qemu set the flag and ack the interrupt from the host side. Any example about it will be highly appreciated.

Thanks once again for your response

Regards
Aji




> -----Original Message-----
> From: dor.laor-atKUWr5tajBWk0Htik3J/w@public.gmane.org
> Sent: Tue, 7 Aug 2007 14:53:01 -0700
> To: aji007-BoNl9JPmOHUAvxtiuMwx3w@public.gmane.org, kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
> Subject: RE: [kvm-devel] DOR : Example for injecting the interrupt to the
> guest
> 
> >Hello Dor,
>> 
> >Can you please point to an example that injects interrupts via
> userspace
> >?
>> 
> >I am running QNX as Guest and Linux as Host. One of my QNX application
> >(Guest application), expects an interrupt from the Hardware.
>> 
> >Now as I understand this, I need to write a driver on the host side to
> >get the interrupt and somehow inject the interrupt to guest OS. But I
> am
> >not sure how to signal the KVM about the arrival of interrupt, without
> >breaking anything.
>> 
> >Ghaskins, suggested your name in kvm-irc. I have pasted relevant part
> of
> >it for your reference.
>> 
> >Your early response will be highly appreciated,
>> 
> >Thanking you
>> 
> >Aji
> 
> Actually we're in the middle of developing pci pass through support for
> enabling
> physical device pass through for guests. It's work in progress but
> eventually we'll
> post the code to the list.
> In our case, maybe yours too, we need to first receive the irq in the
> host, mask it
> and inject it to the guest. Only after the guest acks the irq it should
> be cleared in the host.
> That's the general scheme although there are some hacks in order to pass
> possible deadlocks that
> might be caused by shared irq device.
> 
> Anyway, the relativly easy part is to inject the irq to the guest.
> As Gregory soon the pic/apic/ioapic will move into the kernel and it
> will be easier.
> Until then you can send a signal from the kernel to qemu's main thread
> (get_pid also recommended for safety).
> The signal handler in qemu only sets a flag and schedules a qemu_bh
> (like the kernel's bottom half).
> The bh handler call the pci_set_irq of the right device. You can also
> use the apic/ioapic directly too.
> 
> What's the nature of the project? We can send you some early code
> samples.
> --Dor
> 
>> 
> >10:36 < aji003> the virtual driver is a part of kvm...and so it runs in
> >the host
> >10:36 < ghaskins> ok, so yes you are correct
> >10:36 < ghaskins> the host side would know the real vector of the
> >physical device and would be registered in the host IDT
> >10:36 < aji003> By virtual driver I mean, the driver I have developed
> so
> >that the guest app can interact with the physical hardware
> >10:36 < ghaskins> it would then probably do something like proxy the
> >interrupts into the guest
> >10:37 < ghaskins> ok, i understand you now
> >10:37 < ghaskins> so your proxy/virtual driver would get the real
> >interrupt...you then would want to inject it into the guest as a
> virtual
> >interrupt
> >10:37 < aji003> yes thatz what I wanted to do..sorry if i confused you
> >10:38 < ghaskins> no problem..its clear now
> >10:38 < ghaskins> so I assume you already know how to write your
> virtual
> >driver and register it with linux with the write vector, etc
> >10:38 < ghaskins> ?
> >10:38 < ghaskins> and now you just want to know how to inject the
> >interrupt to the guest
> >10:38 < aji003> I did it for I/O and memory mapping, but I am not sure
> >about how to do for interrupt
> >10:41 < ghaskins> so are we on the same page:  your proxy will handle
> >the real vector?
> >10:42 < aji003> KVM has a virtualised 8259 driver
> >10:43 < ghaskins> yeah, but that code is also in flux right now too
> >10:43 < ghaskins> as of right now, the interrupt infrastructure is all
> >in userspace/QEMU
> >10:43 < ghaskins> its in the process of being moved down into the
> kernel
> >10:44 < ghaskins> at that point it will be much easier to inject
> >interrupts from the kernel, which it sounds like you might need to do
> >10:44 < aji003> ok
> >10:44 < aji003> so with qemu, itz not possible ?
> >10:44 < ghaskins> but as a high level overview, there are emulated
> 8259s
> >and APICs
> >10:45 < ghaskins> well, it should be possible...its just more difficult
> >10:45 < aji003> ok..
> >10:45 < ghaskins> I think Dor has written a driver that utilizes the
> >userspace interrupt stuff as you would need to
> >< ghaskins> I think Dor has written a driver that utilizes the
> userspace
> >interrupt stuff as you would need to
> >10:45 < aji003> Dor ?
> >10:46 < aji003> I am quite new to linux and KVM
> >10:46 < ghaskins> He's one of the Qumranet guys...if he is not here on
> >IRC just hit the list
> >10:46 < ghaskins> kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
> >10:46 < ghaskins> he can probably point you to an example of his that
> >injects interrupts via userspace
> >10:46 < aji003> ok
> >10:47 < ghaskins> and it will all get a little simplified in a few
> weeks
> >when the in-kernel stuff merges
> >10:47 < aji003> Thanks ghaskins
>> 
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Re: FW: RE: DOR : Example for injecting the interrupt to the guest

[Dong, Eddie]

kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org wrote:
> Hello Dor,
> 
> Thank you so much for the quick reply.
> 
> My project is to run a qnx4.4 legacy application (which talks
> to custom made hardware) on virtualized environment. I am
> using KVM for that and am able to read and write to the actual
> hardware. I used serial driver in qemu as a reference to
> develop my custom virtual driver. Let me know what specific
> details you want to know.
> 
> I know fairly well to trap the interrupt in the host side
> (linux). What I would require is some example on how to modify
> the qemu part of the code, so that it the qemu set the flag

Let Qemu set the flag is not that stright forward, it will impact the
performance dramatically. In kernel irqchip will help u on this, but the
foundmental 
stuff to support either VT-d or directly hardware pass thru is still
under going. 
So you probably have to wait for this :-(

BTW, is this hardware shared among different VMs or dedicate to each VM?

> and ack the interrupt from the host side. Any example about it
> will be highly appreciated.
> 
> Thanks once again for your response
> 
> Regards
> Aji
> 
> 
Thx, eddie

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Re: FW: RE: DOR : Example for injecting the interrupt to the guest

[Dor Laor]

>> Hello Dor,
>>
>> Thank you so much for the quick reply.
>>
>> My project is to run a qnx4.4 legacy application (which talks
>> to custom made hardware) on virtualized environment. I am
>> using KVM for that and am able to read and write to the actual
>> hardware. I used serial driver in qemu as a reference to
>> develop my custom virtual driver. Let me know what specific
>> details you want to know.
>>
>> I know fairly well to trap the interrupt in the host side
>> (linux). What I would require is some example on how to modify
>> the qemu part of the code, so that it the qemu set the flag
>
>Let Qemu set the flag is not that stright forward, it will impact the
>performance dramatically. In kernel irqchip will help u on this, but
the
>foundmental
>stuff to support either VT-d or directly hardware pass thru is still
>under going.
>So you probably have to wait for this :-(

While its not trivial it's still doable even without VT-d.
If the device has no shared irq line with high-irq-rate physical device
there 
won't be bug performance penalty.

>
>BTW, is this hardware shared among different VMs or dedicate to each
VM?

Each physical device is dedicated to specific VM, although theoretically

if you have virtualization support in the device like NetXen it can work
too.

>> and ack the interrupt from the host side. Any example about it
>> will be highly appreciated.
>>
>> Thanks once again for your response
>>
>> Regards
>> Aji
>>
>>
>Thx, eddie

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