linux-kernel - Re: [PATCH] [26/31] CPA: Fix reference counting when changing already changed pages

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Message-Id: <478C8578.76E4.0078.0@novell.com>
Date:	Tue, 15 Jan 2008 09:05:44 +0000
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	<ak@...e.de>
Cc:	<mingo@...e.hu>, <tglx@...utronix.de>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] [26/31] CPA: Fix reference counting when changing
	already changed pages

>+	ref_prot = canon_pgprot(ref_prot);
>+	prot = canon_pgprot(prot);
>+
> 	if (pgprot_val(prot) != pgprot_val(ref_prot)) { 
>...
> 	} else if (level == 4) {
>...
> 	} else {
> 		/*
> 		 * When you're here you either set the same page to PAGE_KERNEL

Doesn't this change require modifying the BUG() here into a BUG_ON() so
that it doesn't trigger if pgprot_val(prot) == pgprot_val(ref_prot) and
level != 4?

>+#define canon_pgprot(p) __pgprot(pgprot_val(p) & __supported_pte_mask)

While I remember you stated the inverse, I continue to think that it'd be
safer to mask out the accessed and dirty flags for the comparisons this
macro is being used for.

Jan

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