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