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

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Message-ID: <CALCETrXT0TJO=UdoEFZ_vv9x+0GqQ6bqkrec5-H26_in3ZrqnA@mail.gmail.com>
Date:	Fri, 10 Jul 2015 07:39:53 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Ingo Molnar <mingo@...nel.org>, Brian Gerst <brgerst@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	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 Fri, Jul 10, 2015 at 4:16 AM, Paolo Bonzini <pbonzini@...hat.com> wrote:
>
>
> On 09/07/2015 20:33, Andy Lutomirski wrote:
>> On Wed, Jul 8, 2015 at 10:59 PM, Ingo Molnar <mingo@...nel.org> wrote:
>
>> The big downside of that, or of writing a more ad-hoc emulator, is
>> understanding what the semantics of all the weird vm86plus stuff is
>> supposed to be in the first place.
>
> Do you mean VIF/VIP and the other vm86 mode extensions?  Or is vm86plus
> something in Linux?

Something in Linux written for DOSEMU's benefit.  I don't really
understand what it encompasses.  Oddly, Linux doesn't use the virtual
mode extensions.  Instead, it emulates them (but probably not very
well).  So STI manipulates a fake VIF flag and checks a fake VIP flag.

There's also a huge hack involving 0xA0000.

--Andy
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