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

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Date:	Wed, 8 Aug 2007 10:01:45 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Andi Kleen <andi@...stfloor.org>
cc:	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


--
On Wed, 8 Aug 2007, Andi Kleen wrote:

> > 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.

For now it does ignore them. But that's something to work on
for later versions of lguest64.  I want lguest out in the public and
working for the general case. I don't plan on ignoring the paranoid
section forever. But it's more on an anomaly for now. But you are right, I
want the debug stuff working. But I also need to walk before I can run ;-)


>
> >
> > >>  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.

Ah, OK, I assumed you were talking about just the previous code. But
rereading your post, I see it was more general.  Sorry, for the
miscommunication.

-- Steve

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