linux-kernel - Re: [PATCH 18/25] [PATCH] turn priviled operations into macros in entry.S

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Date:	Wed, 8 Aug 2007 15:29:26 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Glauber de Oliveira Costa <gcosta@...hat.com>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	rusty@...tcorp.com.au, mingo@...e.hu, chrisw@...s-sol.org,
	jeremy@...p.org, avi@...ranet.com, anthony@...emonkey.ws,
	virtualization@...ts.linux-foundation.org, lguest@...abs.org
Subject: Re: [PATCH 18/25] [PATCH] turn priviled operations into macros in entry.S

> When I said "this part of the code I don't fully understand" I was not
> talking about entry.S.  I understand entry.S very well, but the comment
> was originally on the paranoid_restore code. Which I thought had to deal
> with NMIs and such that I didn't worry about that I simply did the
> default.

The paranoid path is used for more than just NMIs; it's also used for MCEs,
stack faults, double faults or debug exceptions. Anything that might
happen with a invalid stack or unknown GS state or system in other unknown
state.

If you can guarantee your hypervisor never injects any of those it could be ignored; 
but at least losing debug exceptions would be probably not nice.

> 
> >>  paranoid_restore\trace:
> >>       RESTORE_ALL 8
> >> -     iretq
> >> +     INTERRUPT_RETURN
> >
> >I suspect Xen will need much more changes anyways because of its
> >ring 3 guest. Are these changes sufficient for lguest?

This was really a general comment not especially applying to the 
paranoid path.

-Andi

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