Re: [Xen-devel] [PATCH-4.5 0/4] remove maintenance interrupts

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 07/02/14 18:56, Stefano Stabellini wrote:
> Hi all,
Hi Stefano,

> this patch series removes any needs for maintenance interrupts for both
> hardware and software interrupts in Xen.
> It achieves the goal by using the GICH_LR_HW bit for hardware interrupts
> and by checking the status of the GICH_LR registers on return to guest,
> clearing the registers that are invalid and handling the lifecycle of
> the corresponding interrupts in Xen data structures.
After reading your patch series I see a possible race condition with the 
timer interrupt.
As you know, Xen can re-inject the timer interrupt before the previous 
one is EOIed. As it's the timer, the IRQ is injected on the current 
running VCPU.
vgic_vcpu_inject_irq(timer)
  -> IRQ already visible to the guest -> set PENDING
return to guest context
<--------------------- Guest EOI the IRQ
.... few milleseconds
going to hyp mode
  -> doing stuff
  -> reinject the timer IRQ

If I'm not mistaken, with your solution, the next IRQ can be delayed for 
few milliseconds. That could be fixed by updating the Lrs.
--
Julien Grall

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