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Date: Tue, 15 Aug 2017 20:02:32 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>,
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Subject: Re: [Xen-devel] [tip:x86/platform] x86/hyper-v: Use hypercall for
 remote TLB flush
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On Fri, 11 Aug 2017 14:07:14 +0200
Peter Zijlstra <peterz@infradead.org> wrote:

> It goes like:
> 
> 	CPU0			CPU1
> 
> 	unhook page
> 				cli
> 				traverse page tables
> 	TLB invalidate --->	<IF clear, therefore CPU0 waits>
> 				sti
> 				<IPI>
> 				 TLB invalidate
> 			<------	 complete

I guess the important part here is the above "complete". CPU0 doesn't
proceed until its receives it. Thus it does act like
cli~rcu_read_lock(), sti~rcu_read_unlock(), and "TLB invalidate" is
equivalent to synchronize_rcu().

[ this response is for clarification for the casual observer of this
  thread ;-) ]

-- Steve

> 				</IPI>
> 	free page
> 
> So the CPU1 page-table walker gets an existence guarantee of the
> page-tables by clearing IF.