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From: Andy Lutomirski <luto@amacapital.net>
Date: Fri, 10 Jul 2015 07:39:53 -0700
Message-ID: <CALCETrXT0TJO=UdoEFZ_vv9x+0GqQ6bqkrec5-H26_in3ZrqnA@mail.gmail.com>
Subject: Re: [PATCH] x86/kconfig/32: Mark CONFIG_VM86 as BROKEN
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>, Brian Gerst <brgerst@gmail.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Oleg Nesterov <oleg@redhat.com>, Kees Cook <keescook@chromium.org>,
        Peter Zijlstra <peterz@infradead.org>, Borislav Petkov <bp@alien8.de>
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On Fri, Jul 10, 2015 at 4:16 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>
>
> On 09/07/2015 20:33, Andy Lutomirski wrote:
>> On Wed, Jul 8, 2015 at 10:59 PM, Ingo Molnar <mingo@kernel.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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