Re: [Xen-devel] [PATCH 1/4] xen/arm: gic: Ensure we have an ISB between ack and do_IRQ()

[Julien Grall <julien.grall@xxxxxxx>]

Hi Andrii,

On 03/12/2018 12:58, Andrii Anisov wrote:
> On 03.12.18 14:17, Julien Grall wrote:
> > No. I meant that I would be happy with that and I think should also suit you.
> Great!
>
> > There are no isb() in do_trap_irq(). So did you mean gic_interrupt()?
> Right you are.
>
> > But then, I am not sure why you want to avoid the isb() in the guest path.
> Well, as I remember, and the commit message says, it is needed to get peripheral 
> register to be updated before interrupt handler reads them for interrupt 
> handling :)
> About guest irqs, we, actually, do not handle them, just rise a notification to 
> guest that it needs handling. Thus that synchronization is not required in a 
> guest interrupt processing path.
Possibly, but I would prefer to keep the isb() in the current position. It 
catches all the handlers so less risk for missing the isb() in the future. Do 
you see any performance drop?
Cheers,

--
Julien Grall

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