linux-kernel - Re: [PATCH] mm: don't lose the SOFT

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Message-Id: <20140129121859.07da0df20daea6a1581e709a@linux-foundation.org>
Date:	Wed, 29 Jan 2014 12:18:59 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andrey Vagin <avagin@...nvz.org>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Cyrill Gorcunov <gorcunov@...nvz.org>, criu@...nvz.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Borislav Petkov <bp@...e.de>,
	Wen Congyang <wency@...fujitsu.com>
Subject: Re: [PATCH] mm: don't lose the SOFT_DIRTY flag on mprotect

On Thu, 30 Jan 2014 00:04:59 +0400 Andrey Vagin <avagin@...nvz.org> wrote:

> The SOFT_DIRTY bit shows that the content of memory was changed
> after a defined point in the past. mprotect() doesn't change the
> content of memory, so it must not change the SOFT_DIRTY bit.
> 
> This patch does nothing with _PAGE_SWP_SOFT_DIRTY, becase pte_modify()
> is called only for present pages.

Standard complaint: when fixing a bug, please describe the end-user
visible effects of that bug.

afaict the effects are minor: snapshotting will save/copy more pages
than it needs to, but there will be no malfunction.  Hence a -stable
backport is unneeded.  Agree?


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