linux-kernel - Re: [PATCH] x86: Plug racy xAPIC access of CPU hotplug code

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Message-ID: <20140127202252.GA11821@two.firstfloor.org>
Date:	Mon, 27 Jan 2014 21:22:52 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Jan Kiszka <jan.kiszka@...mens.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: Plug racy xAPIC access of CPU hotplug code

On Mon, Jan 27, 2014 at 08:14:06PM +0100, Jan Kiszka wrote:
> apic_icr_write and its users in smpboot.c were apparently written under
> the assumption that this code would only run during early boot. But
> nowadays we also execute it when onlining a CPU later on while the
> system is fully running. That will make wakeup_cpu_via_init_nmi and,
> thus, also native_apic_icr_write run in plain process context. If we
> migrate the caller to a different CPU at the wrong time or interrupt it
> and write to ICR/ICR2 to send unrelated IPIs, we can end up sending
> INIT, SIPI or NMIs to wrong CPUs.
> 
> Fix this by disabling interrupts during the write to the ICR halves and
> disable preemption around waiting for ICR availability and using it.

If you just want to disable migration use get_cpu()/put_cpu()

-Andi
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