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

[Ivan Pavic <ivan.pavic2@xxxxxx>]

On 07/05/2017 02:55 PM, Julien Grall wrote:
> 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.
    Yes, I've got message only in domain_destroy.
> 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,
    Regards,

    Ivan Pavic


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