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Re: [Xen-devel] 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 <sstabellini@xxxxxxxxxx>
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 
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 
the interrupt would be through even channel.

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

When interrupts comes, the dom0 will handle that. Then forward the interrupt to 
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 

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?


Julien Grall

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