Re: [Xen-users] Spurious Interrupts on guest OS

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 30 May 2014, Ian Campbell wrote:
> On Fri, 2014-05-30 at 02:40 +0000, Kapania, Ashish wrote:
> > Hi All,
> 
> Copying Stefano who has a series in progress which I have a feeling
> includes addressing some spurious interrupt issues.
> 
> > 
> >  
> > 
> > I am trying to run a RTOS as a guest on a OMAP5432 evm and am seeing a
> > spurious interrupt problem when programming the virtual timer
> > interrupts. My RTOS test case uses the A15 Virtual timer to create a
> > timer instance. Once programmed, the virtual timer interrupt is
> > injected into my guestâs virtual CPU interface as expected and the
> > interrupt is also forwarded to my guest. At this point, my RTOSâs IRQ
> >  service routine is invoked which among other things reads GICV_IAR
> > register to acknowledge the interrupt and then re-enables IRQs (to
> > support nested interrupts) before calling the timer handler which is
> > suppose to program the CNTV_CVAL register for the next tick. I notice
> > that as soon as interrupts are re-enabled, the ISR is interrupted and
> > the IRQ service routine is called again. However, this time GICV_IAR
> > register returns 1023. Once the ISR detects a spurious interrupt and
> > returns, it gets interrupted again with another spurious interrupt. I
> > see that the guest is flooded with these spurious interrupts and is
> > not able to complete servicing the original virtual timer interrupt.
> > 
> >  
> > 
> > If I disable nesting (i.e. do not re-enable IRQs in my service
> > routine), everything works as expected which makes me wonder if the
> > spurious interrupts are related to the virtual timer. I tried adding a
> > debug print in vgic_vcpu_inject_irq to see if xen was injecting some
> > high priority interrupt but found that xen only injects a single
> > virtual timer PPI.
> > 
> >  
> > 
> > Has anyone seen this behavior or has suggestions on how to debug this
> > problem further ?

Hi Ashish,
yes, I have seen this behaviour with a FreeRTOS guest. This patch series
should fix the issue:

http://marc.info/?l=xen-devel&m=140076202414100

A git url is available at the bottom of the email.

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