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

[Peng Fan <peng.fan@xxxxxxx>]

Hi Julien

> -----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
> <andre.przywara@xxxxxxx>
> 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
> >> <sstabellini@xxxxxxxxxx>
> >> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; Andre Przywara
> >> <andre.przywara@xxxxxxx>
> >> 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
> 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 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?

Yes.

> 
> 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
Virtualization. I use generic_handle_irq() when frontent received the forwarded 
interrupt from dom0
in a eventchannel interrupt, but no work.

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.

Thanks,
Peng.

> 
> Cheers,
> 
> --
> Julien Grall
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