Re: [Xen-devel] Possible bug on ARM with irq passthrough

[Julien Grall <julien.grall@xxxxxxx>]

Hi Ivan,

On 05/07/17 13:36, Ivan Pavic wrote:
> On 07/05/2017 01:27 PM, Julien Grall wrote:
> > On 04/07/17 21:20, Ivan Pavić2 wrote:
> > > Hello,
> > Hi Ivan,
> >
> > > I'm testing IRQ latency on exynos5422. I'm using Xen 4.10-unstable. I
> > > used device passthrough for SPI irq 64. For guest domain I used
> > > FreeRTOS. When I use credit scheduler after destruction of domain,
> > > IRQ is released. I changed scheduler to credit2 and rtds at boot time
> > > and IRQ wasn't released after destruction. xl create
> > > dom-free-rtos.cfg fails with:
> > >
> > > libxl: error: libxl_create.c:1278:domcreate_launch_dm: Domain
> > > 5:failed give domain access to irq 64: Device or resource busy
> > >
> > > This is very strange because it doesn't happen with credit scheduler.
> > > This is output of xl dmesg:
> > >
> > > (XEN) IRQ 64 is already used by domain 1
> > >
> > > Everything works first time but when I destroy domain and try to
> > > create again it fails. It works normally with credit scheduler. In
> > > dom-free-rtos.cfg:
> > > ...
> > > irqs = [64]
> > > ....
> > The Domain 1 still seems to be alive, you can confirm by via "xl
> > list". You said it works with credit but not credit2. I think you hit
> > the bug described in [1].
> I checked xl-list. There is no domain with id 1, only dom0. Also I tried
> xenctx 1 which resulted in
>     xc_domain_getinfo: No such process
>
> Same problem is with rtds scheduler. As I said, no problem with credit
> scheduler.
IRQs assigned to a domain will be released by domain_vgic_free() when 
calling release_guest_irq(). This is called by Xen when the domain is 
fully destroyed.
It might be possible the domain is waiting to be fully destroyed, and 
therefore hidden from the toolstack. Can you check if the domain is been 
destroyed by Xen. You can add printk in domain_destroy and 
complete_domain_destroy.
 * domain_destroy is called when there is no more reference on the 
domain (see put_domain)
 * complete_domain_destroy is called when RCU is quiescent

If you got a message in the former, but not the latter. Then you hit the 
bug described in my previous e-mail.
This would happen if some of the pCPUs are idle states (using wfi).r.
The main difference between credit1 and credit2 (I am not sure for RTDS) 
is there are IPI traffic with credit1 on idle pCPU because of the ticker.
> > Dario, do you have any status on this bug? I think we should consider
> > it as a blocker for Xen 4.10.
> >
> > Cheers,
> >
> > [1]
> > https://lists.xenproject.org/archives/html/xen-devel/2017-02/msg00138.html
Cheers,

--
Julien Grall

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