Re: [Xen-devel] [PATCH v2] gic: drop interrupts enabling on interrupts processing

[Andrii Anisov <andrii.anisov@xxxxxxxxx>]

Hello Julien,

On 31.05.19 20:11, Julien Grall wrote:

> Here my take on the commit message:
>
> gic_interrupt() was implemented using a loop to limit the cost of the trap if 
> there are multiple interrupts pending.
>
> At the moment, interrupts are unmasked by gic_interrupt() before calling do_{IRQ, 
> LPI}(). In the case of handling an interrupt routed to guests, its priority will be 
> dropped, via desc->handler->end() called from do_irq(), with interrupt unmasked.
>
> In other words:
>      - Until the priority is dropped, only higher priority interrupt can be 
> received. Today, only Xen interrupts have higher priority.
>      - As soon as priority is dropped, any interrupt can be received.
>
> This means the purpose of the loop in gic_interrupt() is defeated as all 
> interrupts may get trapped earlier. To reinstate the purpose of the loop (and 
> prevent the trap), interrupts should be masked when dropping the priority.
>
> For interrupts routed to Xen, priority will always be dropped with interrupts 
> masked. So the issue is not present. However, it means that we are pointless 
> try to mask the interrupts.
>
> To avoid conflicting behavior between interrupt handling, gic_interrupt() is 
> now keeping interrupts masked and defer the decision to do_{LPI, IRQ}.
It is OK with me.

Are you waiting from me more of

> [ Details to be added once you give more ground ]
?

--
Sincerely,
Andrii Anisov.

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