linux-kernel - Re: [PATCH] x86/kconfig/32: Mark CONFIG

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Message-ID: <CA+55aFyZ9xJwrq9R-cucY6zJeG1NiiSdJOyfyYRvE95t6wn=Nw@mail.gmail.com>
Date:	Wed, 8 Jul 2015 10:55:21 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Arjan van de Ven <arjan@...ux.intel.com>,
	Andy Lutomirski <luto@...nel.org>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Kees Cook <keescook@...omium.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH] x86/kconfig/32: Mark CONFIG_VM86 as BROKEN

On Wed, Jul 8, 2015 at 10:49 AM, Andy Lutomirski <luto@...capital.net> wrote:
>
> I don't know how to tell whether something is trying to use real mode,
> but I can play this just fine in DOSEMU on my 64-bit laptop:

So a 64-bit distro obviously will never have used vm86 mode - it
doesn't work there. Never has. There's no sane way to get to vm86 mode
from long mode, that's just how the 64-bit extensions worked.

(64-bit hardware obviously does support vm86 mode, but you have to
play games with mixing long mode and CPL0 32-bit protected mode to get
there, and we never did that).

It's the 32-bit distros I would worry about. The ones that may have
well disabled emulation, because they have vm86 mode enabled.

                 Linus
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