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

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

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 ?
> 
>  
> 
> Thanks,
> 
> Ashish
> 
>  
> 
> My xen build info:
> 
> I am using xen 4.5-unstable and am at
> 8cfc8e520679e029bed51ccc2540a136fc0fbd9b commit. My RTOS image is an
> elf image and in order to make elf loading work, I have also applied
> the following 2 patches as suggested in this thread ->
> http://lists.freebsd.org/pipermail/freebsd-xen/2014-January/001974.html. 
> These patches should not affect the gic behavior but thought I should mention 
> them just in case:
> 
> https://patches.linaro.org/22228/
> 
> https://patches.linaro.org/22227/
> 
>  
> 
> 
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> http://lists.xen.org/xen-users



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