linux-kernel - Re: How to know if there is a pending interrupt when they are masked?

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <alpine.DEB.2.21.1902141620510.1561@nanos.tec.linutronix.de>
Date:   Thu, 14 Feb 2019 16:35:05 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
cc:     Marc Zyngier <Marc.Zyngier@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: How to know if there is a pending interrupt when they are
 masked?

On Thu, 14 Feb 2019, Daniel Lezcano wrote:
> today we have the possibility to mask the local interrupt with the
> command local_irq_disable / local_irq_enable.
> 
> The power management path disables the local interrupt in order to
> initiate a power down sequence. If there is a pending interrupt this one
> will make the power down function to abort, thus exiting right after
> calling the shutdown function after costly operations. It could be
> interesting to check if there is a pending interrupt before initiating
> the power down sequence.
> 
> Is there a way to know if there is a pending interrupt on the current
> CPU when the local interrupt are disabled? Something like,
> local_irq_pending() function ?

We have nothing like that today, but it would be possible to implement this
at least on x86 by peeking the local APIC registers.

OTOH, the question is whether it's worth the trouble because the interrupt
could come in right after the query and the same issue which you want to
address persists. It only makes sense if it reduces the time window so
significantly that it actually matters.

Thanks,

	tglx