linux-kernel - Re: [PATCH v5 1/4] x86/signal/64: Add a comment about sigcontext->fs and gs

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Message-ID: <20160217110522.GA30222@gmail.com>
Date:	Wed, 17 Feb 2016 12:05:22 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Stas Sergeev <stsp@...t.ru>
Cc:	Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Brian Gerst <brgerst@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>, Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH v5 1/4] x86/signal/64: Add a comment about sigcontext->fs
 and gs


* Stas Sergeev <stsp@...t.ru> wrote:

> 17.02.2016 10:21, Ingo Molnar пишет:
> > 
> > * Andy Lutomirski <luto@...nel.org> wrote:
> > 
> >> +	 * If the kernel ever adds explicit fs, gs, fsbase, and gsbase
> >> +	 * save/restore, it will most likely need to be opt-in and use
> >> +	 * different context slots.
> > 
> > Btw., that's not necessarily true: it could also be made opt-out, and a 
> > modify_ldt() or any other cleanly identifiable legacy usage/signature that is 
> > associated with DOSEMU might trigger the opt-out automatically as well.
> But there are the new versions of dosemu that still use
> "modify_ldt() or any other cleanly identifiable legacy usage/signature"
> and yet wants a new functionality.
> Please don't go for such an unreliable heuristic.

Only if implemented dumbly.

Implemented intelligently there would be 3 runtime states: enabled, disabled, 
automatic. New DOSEMU would explicitly enable it, which would override any 
automatic defaults.

But note that I was only pointing out that the comment is needlessly restrictive. 
Anyway, I have applied Andy's patches.

Thanks,

	Ingo