linux-kernel - Re: [PATCH 0/6] x86/cpu hotplug: Wake up offline CPU via mwait or nmi

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Date:	Wed, 06 Jun 2012 17:48:40 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	paulmck@...ux.vnet.ibm.com, Thomas Gleixner <tglx@...utronix.de>,
	"Luck, Tony" <tony.luck@...el.com>,
	"Yu, Fenghua" <fenghua.yu@...el.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Ingo Molnar <mingo@...e.hu>, H Peter Anvin <hpa@...or.com>,
	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	"Mallick, Asit K" <asit.k.mallick@...el.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	x86 <x86@...nel.org>, linux-pm <linux-pm@...r.kernel.org>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
Subject: Re: [PATCH 0/6] x86/cpu hotplug: Wake up offline CPU via mwait or
 nmi

On Wed, 2012-06-06 at 08:23 -0700, Arjan van de Ven wrote:
> btw TLB invalidation I think is a red herring in this discussion
> (other than "global PTEs" kind of kernel pte changes);
> at least on x86 this is not happening for a long time; if a CPU is
> really idle (which means the CPU internally flushes the tlbs anyway),
> Linux also switches to the kernel PTE set so there's no need for a flush
> later on. 

This is about isolation, not idle. If you share a mm across your
isolation barrier you get TLB invalidates, its unavoidable. The solution
is not sharing the mm -- which is a perfectly usable solution.
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