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To: Andrea Arcangeli <andrea@suse.de>
cc: Andi Kleen <ak@muc.de>, john stultz <johnstul@us.ibm.com>,
       Linus Torvalds <torvalds@transmeta.com>,
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       george anzinger <george@mvista.com>,
       Stephen Hemminger <shemminger@osdl.org>,
       Bill Davidsen <davidsen@tmr.com>
Subject: Re: [PATCH] linux-2.5.43_vsyscall_A0 
In-Reply-To: Your message of "Sat, 19 Oct 2002 07:01:39 +0200."
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Date: Sat, 19 Oct 2002 18:43:28 -0500
From: Jeff Dike <jdike@karaya.com>
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andrea@suse.de said:
> the sysctl would replace the vsyscall fixmap fixmap entry for the
> current cpu enterely at switch_to time, I certainly don't want to add
> not necessary branches in the core vsyscall code.  Doing it globally
> is zerocost but it would probably need privilegies as said, per-task
> could be more dynamic without privilegies and it would be an unlikely
> branch added in switch_to, still a very low cost so still acceptable. 

If I'm understanding this (and reading the code) correctly, this would
allow UML to specify that, for a given process, it should have a page of
its choosing mapped into the vsyscall area.  Correct?

If so, I can go along with this.  It makes vsyscalls virtualizable, and thus
available to UML, which needs them more than the other arches :-)

The one suggestion I'd make is to make it per-mm rather than per-task and 
put it in switch_mm rather than switch_to.

				Jeff

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