Re: [v6 PATCH 00/21] x86: Enable User-Mode Instruction Prevention

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On Wed, 2017-03-29 at 23:55 +0300, Stas Sergeev wrote:
> 29.03.2017 07:38, Ricardo Neri пишет:
> >> Probably you could also remove
> >> the sldt and str emulation for protected mode, because,
> >> as I understand from this thread, wine does not
> >> need those.
> > I see. I would lean on keeping the emulation because I already
> > implemented it :), for completeness, and because it is performed in a
> > single switch. The bulk of the emulation code deals with operands.
> But this is not for free.
> As Andy said, you will then need a syscall and
> a feature mask to be able to disable this emulation.
> And AFAIK you haven't implemented that yet, so
> there is something to consider.

Right, I see your point.

> >>>> You know the wine's
> >>>> requirements now - they are very small. And
> >>>> dosemu doesn't need anything at all but smsw.
> >>>> And even smsw is very rare.
> >>> But emulation is still needed for SMSW, right?
> >> Likely so.
> >> If you want, I can enable the logging of this command
> >> and see if it is used by some of the DOS programs I have.
> > It would be great if you could do that, if you don't mind.
> OK, scheduled to the week-end.
> I'll let you know.


> >> But at least dosemu implements it, so probably it is needed.
> > Right.
> >
> >> Of course if it is used by one of 100 DOS progs, then there
> >> is an option to just add its support to dosemu2 and pretend
> >> the compatibility problems did not exist. :)
> > Do you mean relaying the GP fault to dosemu instead of trapping it and
> > emulating it in the kernel?
> Yes, that would be optimal if this does not severely break
> the current setups. If we can find out that smsw is not in
> the real use, we can probably do exactly that. 
> But other
> instructions are not in real use in v86 for sure, so I
> wouldn't be adding the explicit test-cases to the kernel
> that will make you depend on some particular behaviour
> that no one may need.

> My objection was that we shouldn't
> write tests before we know exactly how we want this to work.
OK, if only SMSW is used then I'll keep the emulation for SMSW only.

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