Re: [RFC/PATCH 5/7] x86/vm86: Teach handle_vm86_trap to return to 32bit mode directly

[Andy Lutomirski]

On Wed, Jul 8, 2015 at 12:24 PM, Andy Lutomirski <luto@xxxxxxxxxx> wrote:
> The TIF_NOTIFY_RESUME hack it was using was buggy and unsupportable.
> vm86 mode was completely broken under ptrace, for example, because
> we'd never make it to v8086 mode.
>
> This code is still a huge, scary mess, but at least it's no longer
> tangled with the exit-to-userspace loop.

This patch is incorrect.  Brian, what's the ETA for your vm86 cleanup?
 If it's very soon, then I'll see if I can rely on it.  If not, I'll
have to come up with a way to fix this patch.

Grr.  The kernel state when handle_vm86_trap is called is absurd right
now.  Somehow we're supposed to survive do_trap, send a signal
corresponding to the outside-vm86 state, and exit vm86 cleanly (with
ax = 0), all before returning to user mode.  I doubt these semantics
are even intentional.

This code sucks.

--Andy
--
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/