Re: RFC: userspace exception fixups

[Jarkko Sakkinen]

On Tue, Nov 20, 2018 at 07:19:37AM -0800, Andy Lutomirski wrote:
> What is "#GP with EPCM"?  We certainly don't want to react to #UD in

A typo. Meant #PF with PF_SGX set i.e. EPCM conflict.

> general by mucking with some regs and retrying -- that will infinite
> loop and confuse everyone.  I'm not even 100% convinced that decoding
> the insn stream is useful -- AEP can point to something that isn't
> ENCLU.

In my return-to-AEP approach to whole point was not to do any decoding
but instead have something else always in the AEP handler than just
ENCLU.

No instruction decoding. No RIP manipulation.

> IOW the kernel needs to know *when* to apply this special behavior.
> Sadly there is no bit in the exception frame that says "came from
> SGX".

/Jarkko