linux-kernel - Re: x86_64 Question: Are concurrent IPI requests safe?

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Message-ID: <alpine.DEB.2.11.1605091853130.3540@nanos>
Date:	Mon, 9 May 2016 18:54:14 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
cc:	peterz@...radead.org, mingo@...nel.org, akpm@...ux-foundation.org,
	mgorman@...hsingularity.net, mhocko@...nel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: x86_64 Question: Are concurrent IPI requests safe?

On Mon, 9 May 2016, Tetsuo Handa wrote:
> 
> It seems to me that APIC_BASE APIC_ICR APIC_ICR_BUSY are all constant
> regardless of calling cpu. Thus, native_apic_mem_read() and
> native_apic_mem_write() are using globally shared constant memory
> address and __xapic_wait_icr_idle() is making decision based on
> globally shared constant memory address. Am I right?

No. The APIC address space is per cpu. It's the same address but it's always
accessing the local APIC of the cpu on which it is called.

Thanks,

	tglx