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Date:   Mon, 19 Nov 2018 18:02:04 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
To:     Andy Lutomirski <luto@kernel.org>
Cc:     Dave Hansen <dave.hansen@linux.intel.com>,
        "Christopherson, Sean J" <sean.j.christopherson@intel.com>,
        Jethro Beekman <jethro@fortanix.com>,
        Florian Weimer <fweimer@redhat.com>,
        Linux API <linux-api@vger.kernel.org>,
        Jann Horn <jannh@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        X86 ML <x86@kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Rich Felker <dalias@libc.org>, nhorman@redhat.com,
        npmccallum@redhat.com, "Ayoun, Serge" <serge.ayoun@intel.com>,
        shay.katz-zamir@intel.com, linux-sgx@vger.kernel.org,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>
Subject: Re: RFC: userspace exception fixups
Message-ID: <20181119160204.GD13298@linux.intel.com>
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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.

> 2. It starts exposing what looks like a more generic exception
> handling mechanism to userspace, except that it's nonsensical for
> anything other than ENCLU.

Well, I see the user space and namely the run-time the host for the
enclave i.e. middle-man to provide services for emulating instructions
etc.

/Jarkko