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

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Message-ID: <op.v9hbr5xx3l0zgt@mpn-glaptop>
Date:	Fri, 10 Feb 2012 21:13:07 +0100
From:	"Michal Nazarewicz" <mina86@...a86.com>
To:	"Dan Smith" <danms@...ibm.com>
Cc:	akpm@...ux-foundation.org, 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 20:57:31 +0100, Dan Smith <danms@...ibm.com> wrote:
> MN> Commit message says about walk_pte_range() but commit changes
> MN> walk_page_range().
>
> Yep, the issue occurs in walk_pte_range().

OK, it wasn't immediately obvious for me that while loop in walk_page_range()
will actually recover if arguments are not aligned (since pgd_addr_end() caps
returned value).

> The goal was to ensure that
> the external interface to it (which is walk_page_range()) does the check
> and avoids doing the walk entirely. I think the expectation is that
> walk_page_range() is used on aligned addresses. If we put the check in
> walk_pte_range() then only walks with a pte_entry handler would fail on
> unaligned addresses, which is potentially confusing.
>
> MN> So why not change the condition to addr < end?
>
> That would work, of course, but seems sloppier and less precise. The
> existing code was clearly written expecting to walk aligned addresses.

Fair enough.

-- 
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