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From:   Andy Lutomirski <luto@kernel.org>
Date:   Mon, 19 Nov 2018 09:00:08 -0800
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Subject: Re: RFC: userspace exception fixups
To:     Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc:     Andrew Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "Christopherson, Sean J" <sean.j.christopherson@intel.com>,
        Jethro Beekman <jethro@fortanix.com>,
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        Jann Horn <jannh@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
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        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>
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On Mon, Nov 19, 2018 at 8:02 AM Jarkko Sakkinen
<jarkko.sakkinen@linux.intel.com> wrote:
>
> On Mon, Nov 19, 2018 at 07:29:36AM -0800, Andy Lutomirski wrote:
> > 1. The kernel needs some way to know *when* to apply this fixup.
> > Decoding the instruction stream and doing it to all exceptions that
> > hit an ENCLU instruction seems like a poor design.
>
> I'm not sure why you would ever need to do any type of fixup as the idea
> is to just return to AEP i.e. from chosen exceptions (EPCM, #UD) the AEP
> would work the same way as for exceptions that the kernel can deal with
> except filling the exception information to registers.

Sure, but how does the kernel know when to do that and when to send a
signal?  I don't really like decoding the instruction stream to figure
it out.