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From: Marc Zyngier <marc.zyngier@arm.com>
To: Pavel Machek <pavel@ucw.cz>
Cc: <linux-arm-kernel@lists.infradead.org>,
	<linux-kernel@vger.kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH] arm64: Trap WFI executed in userspace
Date: Thu, 20 Sep 2018 23:33:20 +0100	[thread overview]
Message-ID: <86lg7vx0i7.wl-marc.zyngier@arm.com> (raw)
In-Reply-To: <20180920220430.GA27468@xo-6d-61-c0.localdomain>

On Thu, 20 Sep 2018 23:04:30 +0100,
Pavel Machek <pavel@ucw.cz> wrote:
> 
> On Tue 2018-08-07 10:33:26, Marc Zyngier wrote:
> > It recently came to light that userspace can execute WFI, and that
> > the arm64 kernel doesn trap this event. This sounds rather benign,
> > but the kernel should decide when it wants to wait for an interrupt,
> > and not userspace.
> > 
> > Let's trap WFI and treat it as a way to yield the CPU to another
> > process.
> 
> I don't think that's reasonable. Userspace should not be doing that,
> and we do not want to encourage it. SIGILL would be reasonable, I'd
> say.

This ship has already sailed. Sending SIGILL changes the ABI in an
incompatible way. Immediately returning to userspace without doing
anything else (see v2 [1]) is the best we can do without changing the
behaviour of userspace.

Thanks,

	M.

[1] https://patchwork.kernel.org/patch/10562517/

-- 
Jazz is not dead, it just smell funny.

      reply	other threads:[~2018-09-20 22:33 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-07  9:33 Marc Zyngier
2018-08-07 10:05 ` Dave Martin
2018-08-07 10:24   ` Marc Zyngier
2018-08-07 10:30     ` Dave Martin
2018-08-07 12:12       ` Robin Murphy
2018-08-07 13:02         ` Dave Martin
2018-08-08 12:34     ` Catalin Marinas
2018-08-09 12:34       ` Dave Martin
2018-08-09 12:38         ` Will Deacon
2018-08-09 12:47           ` Dave Martin
2018-08-09 13:25             ` Marc Zyngier
2018-09-20 22:04 ` Pavel Machek
2018-09-20 22:33   ` Marc Zyngier [this message]

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