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Subject: Re: [rfc] [patch] kernel hooks
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Richard J Moore <richardj_moore@uk.ibm.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Michael Grundy <vamsi_krishna@in.ibm.com>,
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Date: 03 Oct 2002 15:00:52 +0100
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On Thu, 2002-10-03 at 14:32, Richard J Moore wrote:
> 
> > You must also ensure that the code you are modifying isnt on an IRQ path
> > (if it is you must do spin locks and then be very careful about cross
> > cpu tlb deadlocks). Finally you have no choice but to ensure you never
> > use it on the NMI path
> 
> Why do we need a spinlock? We change one byte, we are not concered about
> when exactly that takes effect, only that there are always valid
> instructions in the pipeline.

Because you are programming for real silicon not for the imaginary
perfect processor. Read the x86 errata