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From: Jamie Lokier <jamie@shareable.org>
To: Roland McGrath <roland@redhat.com>
Cc: Andrew Morton <akpm@digeo.com>,
	torvalds@transmeta.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] i386 uaccess to fixmap pages
Date: Fri, 9 May 2003 13:40:42 +0100	[thread overview]
Message-ID: <20030509124042.GB25569@mail.jlokier.co.uk> (raw)
In-Reply-To: <200305090855.h498t4b12921@magilla.sf.frob.com>

Roland McGrath wrote:
> The address is valid, but above TASK_SIZE.  The purpose of access_ok
> is to say that it's ok to try it and let it fault, because it's a
> user-visible address and not the kernel memory mapped into the high
> part of every process's address space.  The accesses that follow are
> done in kernel mode, so there is no fault for pages marked as not
> user-visible.  The fixmap addresses are > TASK_SIZE and so fail the
> __range_ok test, heretofore making access_ok return false.  Those
> are the code paths leading to EFAULT that I mentioned.
> 
> So far I can't think of a better way to do it.

Why don't you change TASK_SIZE to 0xc0001000 (or so) and place the
user-visible fixmaps at 0xc0000000?

That would have no cost at all.

-- Jamie

  parent reply	other threads:[~2003-05-09 12:28 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-05-09  2:03 [PATCH] i386 uaccess to fixmap pages Roland McGrath
2003-05-09  4:31 ` Andrew Morton
2003-05-09  8:55   ` Roland McGrath
2003-05-09  9:19     ` Andrew Morton
2003-05-09  9:40       ` Roland McGrath
2003-05-09 10:43       ` Roland McGrath
2003-05-09 11:42         ` Dave Jones
2003-05-09 11:55         ` Alan Cox
2003-05-09 12:40     ` Jamie Lokier [this message]
2003-05-09 16:06       ` Linus Torvalds
2003-05-09 16:38         ` Dave Hansen
2003-05-09 15:55           ` Martin J. Bligh
2003-05-09 18:20             ` William Lee Irwin III
2003-05-09 16:48           ` Linus Torvalds
2003-05-09 17:16             ` Dave Hansen
2003-05-10  3:26         ` H. Peter Anvin
2003-05-10 15:31           ` Jamie Lokier
2003-05-10 17:23             ` Ulrich Drepper
2003-05-10 19:23             ` H. Peter Anvin
2003-05-10 20:52               ` Jamie Lokier
2003-05-09 17:28 Chuck Ebbert
2003-05-09 17:49 ` Linus Torvalds

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