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

From: Andrii Anisov <andrii.anisov@gmail.com>
To: Julien Grall <julien.grall@arm.com>, xen-devel@lists.xenproject.org
Cc: Andre Przywara <andre.przywara@arm.com>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Andrii Anisov <andrii_anisov@epam.com>
Subject: Re: [Xen-devel] [PATCH v2] gic: drop interrupts enabling on interrupts processing
Date: Mon, 10 Jun 2019 18:49:29 +0300	[thread overview]
Message-ID: <1388d47c-efd1-b30b-9847-92c343964dfa@gmail.com> (raw)
In-Reply-To: <4d27c123-826d-ad07-ed0a-e7a7517fca62@arm.com>

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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