On Tue, Aug 18, 2020 at 10:15:49AM -0700, Andy Lutomirski wrote: > On Mon, Aug 17, 2020 at 9:24 PM Sean Christopherson > <sean.j.christopherson@xxxxxxxxx> wrote: > > > > Allow userspace to exit the vDSO on interrupts that are acknowledged > > while the enclave is active. This allows the user's runtime to switch > > contexts at opportune times without additional overhead, e.g. when using > > an M:N threading model (where M user threads run N TCSs, with N > M). > > This is IMO rather odd. We don't support this type of notification on > interrupts for normal user code. The fact user code can detect > interrupts during enclave execution is IMO an oddity of SGX, and I > have asked Intel to consider replacing the AEX mechanism with > something more transparent to user mode. If this ever happens, this > mechanism is toast. > > Even without architecture changes, building a *reliable* M:N threading > mechanism on top of this will be difficult or impossible, as there is > no particular guarantee that a thread will get timing interrupts at > all or that these interrupts will get lucky and hit enclave code, thus > triggering an AEX. We certainly don't, and probably never will, > support any corresponding feature for non-enclave code. > > So this seems like an odd, and possibly unsupportable, feature to add. I 100% agree that allowing the user to act on interrupts is weird/fragile. I'll happily kill this off if there's an "official" NAK, but I wanted to force the issue so that we're not stuck in limbo wondering whether or not this should be supported.
