linux-kernel - Re: pipe/page fault oddness.

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Date:	Tue, 30 Sep 2014 12:07:29 -0400
From:	Dave Jones <davej@...hat.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Michel Lespinasse <walken@...gle.com>
Subject: Re: pipe/page fault oddness.

On Tue, Sep 30, 2014 at 12:03:06PM -0400, Rik van Riel wrote:

 > > What kind of CPU is the problematic machine? There was some
 > > question about just how architectural the whole "TLB entry causing
 > > a page fault gets invalidated automatically" really is.
 > 
 > Intel people told me at the time that the guarantee was architectural.
 > I don't know whether other x86 manufacturers know this...
 > 
 > Doing a local tlb flush from ptep_set_access_flags seems appropriate,
 > if that is indeed the issue.
 > 
 > On the other hand, do_wp_page does not seem to do a tlb flush when
 > the old page is reused, so CPUs do get rid of inappropriate TLB
 > entries. We would have noticed do_wp_page not working right :)
 
The puzzling thing is we've had that code change for two years
without issue. This isn't a new machine, so why would it only
be showing up bad effects now ?

	Dave

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