linux-kernel - Re: [patches] new text patching for review

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Date:	Thu, 19 Jul 2007 13:51:51 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Andi Kleen <ak@...e.de>
CC:	patches@...-64.org, Zachary Amsden <zach@...are.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org,
	"S. P. Prasanna" <prasanna@...ibm.com>,
	Chris Wright <chrisw@...s-sol.org>
Subject: Re: [patches] new text patching for review

Andi Kleen wrote:
> Normally there are not that many NMIs or MCEs at boot, but it would
> be still good to avoid the very rare crash by auditing the code first
> [better than try to debug it on some production system later]
>   

Auditing it for what?  If we want to make patching safe against NMI/MCE,
I guess we need to make sure those handlers don't use any pvops, but
that seems unreasonable if they want to poke at MSRs and so on.

> In theory yes, in practice there can be errata of course. There tend 
> to be a couple with self modifying code, especially cross modifying
> (from another CPU) -- but you don't do that.
>   

No, but the pv-ops patching code should have no requirement for
atomicity at all; we shouldn't be trying to patch a live instruction stream.

    J
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