linux-kernel - Re: [PATCH] paravirt.h

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Message-ID: <44EB5A76.9060402@vmware.com>
Date:	Tue, 22 Aug 2006 12:26:46 -0700
From:	Zachary Amsden <zach@...are.com>
To:	Zachary Amsden <zach@...are.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Arjan van de Ven <arjan@...radead.org>, Andi Kleen <ak@....de>,
	virtualization@...ts.osdl.org,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Andrew Morton <akpm@...l.org>,
	Chris Wright <chrisw@...s-sol.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] paravirt.h

Zachary Amsden wrote:

 > I've already implemented the locking and repatching bits for VMI.

Incorrectly, I might add.  The problem case for syscall patching is what 
do you do if there are in-service system calls?  The comparable problem 
here is what if you interrupt code running in the old paravirt-ops, or 
worse, a section of code that you repatch when you do the switch?

That is a really nasty problem.  You need a synchronization primitive 
which guarantees a flat stack, so you can't do it in the interrupt 
handler as I have tried to do.  I'll bang my head on it awhile.  In the 
meantime, were there ever any solutions to the syscall patching problem 
that might lend me a clue as to what to do (or not to do, or impossible?).

Thanks,

Zach
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