linux-kernel - Re: What protects cpu

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Date:	Thu, 05 Apr 2007 14:00:22 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Andi Kleen <ak@...e.de>
CC:	Benjamin LaHaise <bcrl@...ck.org>, Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: What protects cpu_tlbstate?

Andi Kleen wrote:
> The interrupts can only happen when the other CPU is already lazy
> and enter_lazy_tlb would be a nop then.  The flushers itself are
> synchronized by the page_table_lock or the mm semaphore.
>
> Against switch_mm it tries to protect with ordering.
>
> wmb()s are not needed on x86 (ok minus errata on ppro and
> VIA magic mode but which is UP only). That would leave some rmb()s,
> but I don't see any place they would be needed. 
>   

Hm, I was more wondering about simple compiler reordering.  Does the
relative order of setting and reading cpu_tlbstate.state, active_mm and
the mm->cpu_vm_mask matter?

    J
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