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From:   Jethro Beekman <jethro@fortanix.com>
To:     Sean Christopherson <sean.j.christopherson@intel.com>
CC:     Andy Lutomirski <luto@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Rich Felker <dalias@libc.org>, Jann Horn <jannh@google.com>,
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        Carlos O'Donell <carlos@redhat.com>,
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Subject: Re: RFC: userspace exception fixups
Thread-Topic: RFC: userspace exception fixups
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Date:   Fri, 2 Nov 2018 16:56:36 +0000
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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.
>=20
> 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.
>=20

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.=20
SGX-Step)

--
Jethro Beekman | Fortanix


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