linux-kernel - Re: RFC: userspace exception fixups

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Message-ID: <dd455b30-b586-bf5b-2195-cf20c1af9890@fortanix.com>
Date:   Fri, 2 Nov 2018 16:56:36 +0000
From:   Jethro Beekman <jethro@...tanix.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
CC:     Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Rich Felker <dalias@...c.org>, Jann Horn <jannh@...gle.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Florian Weimer <fweimer@...hat.com>,
        Linux API <linux-api@...r.kernel.org>, X86 ML <x86@...nel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "nhorman@...hat.com" <nhorman@...hat.com>,
        "npmccallum@...hat.com" <npmccallum@...hat.com>,
        "Ayoun, Serge" <serge.ayoun@...el.com>,
        "shay.katz-zamir@...el.com" <shay.katz-zamir@...el.com>,
        "linux-sgx@...r.kernel.org" <linux-sgx@...r.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Carlos O'Donell <carlos@...hat.com>,
        "adhemerval.zanella@...aro.org" <adhemerval.zanella@...aro.org>
Subject: Re: RFC: userspace exception fixups

On 2018-11-02 09:52, Sean Christopherson wrote:
> On Fri, Nov 02, 2018 at 04:37:10PM +0000, Jethro Beekman wrote:
>> On 2018-11-02 09:30, Sean Christopherson wrote:
>>> ... The intended convention for EENTER is to have an ENCLU at the AEX target ...
>>>
>>> ... to further enforce that the AEX target needs to be ENCLU.
>>
>> Some SGX runtimes may want to use a different AEX target.
> 
> To what end?  Userspace gets no indication as to why the AEX occurred.
> And if exceptions are getting transfered to userspace the trampoline
> would effectively be handling only INTR, NMI, #MC and EPC #PF.
> 

Various reasons...

Userspace may have established an exception handling convention with the 
enclave (by setting TCS.NSSA > 1) and may want to call EENTER instead of 
ERESUME.

Userspace may want fine-grained control over enclave scheduling (e.g. 
SGX-Step)

--
Jethro Beekman | Fortanix


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