On Wed, Sep 30, 2020 at 07:09:33PM +0100, Andrew Cooper wrote: > Honestly, my advice would be to leave it unprotected for now. Anyone > who managed to figure out the rest of the practical userspace issues > will probably have a much better idea of what can/should be done in this > case. > > If that doesn't sit well with people, then the next best would probably > be LFENCE; CALL *reg/mem; LFENCE to cover as many of the corner cases as > possible without being incompatible with CET. Its not as if this > callback is the slow aspect of entering/exiting SGX mode. > > ~Andrew I tend to agree. We cannot drive changes based on unknown unknowns. And I don't see why we could not add boot time patching of retpoline even after the code is in the mainline kernel, if something ever pushes to that direction. /Jarkko
