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Re: [Xen-devel] Question, How to share interrupt between Doms

On 08/10/2018 03:37, Peng Fan wrote:
Hi Julien

Hi Peng,

-----Original Message-----
From: Julien Grall [mailto:julien.grall@xxxxxxx]
Sent: 2018年10月5日 1:27
To: Peng Fan <peng.fan@xxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; Andre Przywara
Subject: Re: Question, How to share interrupt between Doms

Hi Peng,

On 04/10/2018 02:12, Peng Fan wrote:
-----Original Message-----
From: Julien Grall [mailto:julien.grall@xxxxxxx]
Sent: 2018年10月3日 0:03
To: Peng Fan <peng.fan@xxxxxxx>; Stefano Stabellini
Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; Andre Przywara
Subject: Re: Question, How to share interrupt between Doms

On 02/10/2018 09:32, Peng Fan wrote:
Hi Julien, Stefano,

Hi Peng,

Do you have any suggestions on how to share one interrupt between Doms?

Sharing interrupts are usually a pain. You would need to forward the
interrupts to all the domains using that interrupt and wait for them
to EOI. This has security implications because you don't want DomA to
prevent DomB receiving another interrupt because the previous one has not
been EOIed correctly.

The issue is that a gpio controller has 32 in/out port, however it
only has one
binded interrupt. The interrupt handler needs to check the status
bits to check which port has interrupt coming.
In my case, there are different devices using gpio interrupt that
needs to be
assigned to different doms.

   From what you wrote, it looks like you expect the GPIO controller
to be shared with multiple domains.

I don't think it is safe to do that. You need one domain (or Xen) to
fully manage the controller. All the other domain will have to access
either a virtual GPIO controller or PV one. In the former, interrupt
would be virtual, while the latter the interrupt would be through even

So sharing interrupt should not be necessary. Did I miss anything?

When interrupts comes, the dom0 will handle that. Then forward the
interrupt to domu.
But I did not find a good method to forward the interrupt and hook the
interrupt in domu dts and domu driver.

In Domu, driver needs use request irq and the dts needs interrupt=<xx
xx>. But  when dom0 notify remote, there is no hook in frontend driver and
the other driver interrupt handler.

You say that Dom0 will receive the interrupt. So Dom0 is access directly the
GPIO controller. Right?


What about the guests? Do they access directly the GPIO controller? Or did you
introduce a PV protocol for this?

Guest use PV to access GPIO in Dom0.
When interrupt comes to dom0, the pv use event channel to forward the interrupt 
to Domu,
I did not find a good way to do interrupt forwarding and let domu handle the 
interrupt as without

Do you mean using a SPIs rather than an event channel to deliver the interrupt to the guest?

I use generic_handle_irq() when frontent received the forwarded interrupt from 
in a eventchannel interrupt, but no work.

Do you see any error? Would it be possible to paste logs?

Another issue is in backend, request_threaded_irq for the gpio, some gpio will 
trigger interrupt before
domu could handle the interrupt, this is because gpio default status or some on 
board devices pull up/down
the gpio.

I am not sure to understand the issue with that. It should not be different from the hardware case. Would it be possible to expand it?

Julien Grall

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