linux-kernel - Re: race with page_referenced_one->ptep_test_and_clear

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Message-ID: <47066AD0.4010102@goop.org>
Date:	Fri, 05 Oct 2007 09:48:16 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Keir Fraser <keir@...source.com>
CC:	Hugh Dickins <hugh@...itas.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Zachary Amsden <zach@...are.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Jan Beulich <jbeulich@...ell.com>, Andi Kleen <ak@...e.de>,
	Ken Chen <kenchen@...gle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: race with page_referenced_one->ptep_test_and_clear_young and
 pagetable setup/pulldown

Keir Fraser wrote:
> I didn't think that nobbling config options for particular pv_ops
> implementations was acceptable? I'm rather out of the loop though, and could
> be wrong.
>   

As a workaround it would be OK.  As a dependency, perhaps.

> The PREEMPT_BITS limitation is a good argument for at least taking the pte
> locks in small batches though (small batches is preferable to one-by-one
> since we will want to batch the make-readonly-and-pin hypercall requests to
> amortise the cost of the hypervisor trap).
>   

Hm, that's a good point.  The pagetable permissions changes are batched
more or less asynchronously from the actual loop structure; that will
complicate adding the locking.

       J
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