linux-kernel - Why do we set _PAGE_DIRTY for page tables?

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Message-ID: <5356FCC1.6060807@zytor.com>
Date:	Tue, 22 Apr 2014 16:35:29 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Why do we set _PAGE_DIRTY for page tables?

I just noticed this:

#define _PAGE_TABLE     (_PAGE_PRESENT | _PAGE_RW | _PAGE_USER |       \
                         _PAGE_ACCESSED | _PAGE_DIRTY)
#define _KERNPG_TABLE   (_PAGE_PRESENT | _PAGE_RW | _PAGE_ACCESSED |   \
                         _PAGE_DIRTY)

Is there a reason we set _PAGE_DIRTY for page tables?  It has no
function, but doesn't do any harm either (the dirty bit is ignored for
page tables)... it just looks funny to me.

	-hpa
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