From: "Riley Williams" <Riley@Williams.Name>
To: "Linus Torvalds" <torvalds@transmeta.com>, <davidm@hpl.hp.com>
Cc: <roland@redhat.com>, <linux-kernel@vger.kernel.org>
Subject: Re: [BUG] FIXMAP-related change to mm/memory.c
Date: Fri, 13 Jun 2003 08:28:47 +0100
Message-ID: <BKEGKPICNAKILKJKMHCAIEALEFAA.Riley@Williams.Name>
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Hi Linus, all.

 >> Is it possible to constrain the FIXADDR range on x86/x86-64
 >> (FIXADDR_START-FIXADDR_TOP) such that the entire range is
 >> read-only by user-level?  If so, we could simplify the
 >> permission test like this:

 > Well, you could replace the uses of FIXADDR_START/FIXADDR_TOP
 > with something like FIXADDR_USER_START/FIXADDR_USER_TOP, and
 > then force those to cover only the _one_ user-accessible page.
 >
 > Something like
 >
 >	#define FIXADDR_USER_START (fix_to_virt(FIX_VSYSCALL))
 >	#define FIXADDR_USER_END (FIXADDR_USER_START + PAGE_SIZE)
 >
 > should work. In that case you can drop the page table testing,
 > since we "know" it is safe.

Should FIXADDR_USER_END point to the last byte of the relevant page,
or to the first byte of the following page as per Linus's suggestion?
The above looks like an off-by-one bug to me?

Best wishes from Riley.
---
 * Nothing as pretty as a smile, nothing as ugly as a frown.

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