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

[Julien Grall <julien.grall@xxxxxxx>]

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

--
Julien Grall

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