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

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Message-ID: <52E767C2.2090807@siemens.com>
Date:	Tue, 28 Jan 2014 09:18:10 +0100
From:	Jan Kiszka <jan.kiszka@...mens.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: Plug racy xAPIC access of CPU hotplug code

On 2014-01-27 21:22, Andi Kleen wrote:
> 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()

Fine with me if that is now preferred. Will that be the upstream way of
-rt's migrate_disable()?

Jan

-- 
Siemens AG, Corporate Technology, CT RTC ITP SES-DE
Corporate Competence Center Embedded Linux
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