linux-kernel - Re: [PATCH] Ensure that walk_page_range()'s start and end are page-aligned

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Message-ID: <op.v9hahmw23l0zgt@mpn-glaptop>
Date:	Fri, 10 Feb 2012 20:45:12 +0100
From:	"Michal Nazarewicz" <mina86@...a86.com>
To:	akpm@...ux-foundation.org, "Dan Smith" <danms@...ibm.com>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Ensure that walk_page_range()'s start and end are
 page-aligned

On Fri, 10 Feb 2012 20:39:56 +0100, Dan Smith <danms@...ibm.com> wrote:
> The inner function walk_pte_range() increments "addr" by PAGE_SIZE after

Commit message says about walk_pte_range() but commit changes walk_page_range().

> each pte is processed, and only exits the loop if the result is equal to
> "end". Current, if either (or both of) the starting or ending addresses

So why not change the condition to addr < end?

> passed to walk_page_range() are not page-aligned, then we will never
> satisfy that exit condition and begin calling the pte_entry handler with
> bad data.
>
> To be sure that we will land in the right spot, this patch checks that
> both "addr" and "end" are page-aligned in walk_page_range() before starting
> the traversal.
>
> Signed-off-by: Dan Smith <danms@...ibm.com>
> Cc: linux-mm@...ck.org
> Cc: linux-kernel@...r.kernel.org
> ---
>  mm/pagewalk.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
>
> diff --git a/mm/pagewalk.c b/mm/pagewalk.c
> index 2f5cf10..9242bfc 100644
> --- a/mm/pagewalk.c
> +++ b/mm/pagewalk.c
> @@ -196,6 +196,8 @@ int walk_page_range(unsigned long addr, unsigned long end,
>  	if (addr >= end)
>  		return err;
>+	VM_BUG_ON((addr & ~PAGE_MASK) || (end & ~PAGE_MASK));
> +
>  	if (!walk->mm)
>  		return -EINVAL;
>


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