linux-kernel - Re: [BUGFIX][PATCH] pagemap: set pagemap walk limit to PMD boundary

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Message-ID: <20101122040953.GB3017@spritzera.linux.bs1.fc.nec.co.jp>
Date:	Mon, 22 Nov 2010 13:09:54 +0900
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Jun'ichi Nomura" <j-nomura@...jp.nec.com>,
	Matt Mackall <mpm@...enic.com>
Subject: Re: [BUGFIX][PATCH] pagemap: set pagemap walk limit to PMD boundary

> > @@ -776,7 +777,7 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
> >  		unsigned long end;
> >
> >  		pm.pos = 0;
> > -		end = start_vaddr + PAGEMAP_WALK_SIZE;
> > +		end = (start_vaddr + PAGEMAP_WALK_SIZE) & PAGEMAP_WALK_MASK;
> >  		/* overflow ? */
> >  		if (end < start_vaddr || end > end_vaddr)
> >  			end = end_vaddr;
>
> Ack.
>
> But ALIGN() can't be used ?

ALIGN() returns the same address as the input if it is already aligned,
but what we need here is the next PMD boundary. So something like

                end = IS_ALIGNED(start_vaddr, PAGEMAP_WALK_SIZE) ?
                        start_vaddr + PAGEMAP_WALK_SIZE :
                        ALIGN(start_vaddr, PAGEMAP_WALK_SIZE)          

keeps the semantics, but I don't like it because it's lengthy.

Anyway, thanks for your comment.

Naoya Horiguchi
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