Re: [PATCH] x86/kconfig/32: Mark CONFIG_VM86 as BROKEN

[Linus Torvalds]

On Fri, Jul 10, 2015 at 7:37 AM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>
> Having just written a pile of tests for it, I don't think so, as long as none
> of the syscall slow path stuff is in use :(

It seems that you are thinking that people actually use vm86 mode as a
real Linux mode, and do system calls from it etc.

I'm sure that has happened in some crazy situation (people doing some
random pseudo-BIOS etc), but it's not the common situation at all.

The common situation is that you enter vm86 mode with vm86(), and that
you exit it due to one of the (many) unhandled situations or a signal
or whatever. Yeah,we handle a few sad instructions directly, but most
vm86 exits just return to user mode.

The system call paths just aren't an issue in reality, because they
just aren't used.

And I'm personally violently against Ingo's idea of emulating this
with an instruction emulator. Hell no. That's what user mode does, and
it's fine there. In the kernel, we either support the hardware vm86
mode, or we phase it out because we can show that nobody uses it any
more. None of that "let's emulate it in software" crud.

                      Linus
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/