On 3/24/21 2:26 PM, Andy Lutomirski wrote: >> 3. user space always uses fully uncompacted XSAVE buffers. >> > There is no reason we have to do this for new states. Arguably we > shouldn’t for AMX to avoid yet another altstack explosion.
The thing that's worried me is that the list of OS-enabled states is visible to apps via XGETBV. It doesn't seem too much of a stretch to think that apps will see AMX enabled with XGETBV and them assume that it's on the signal stack. Please tell me I'm being too paranoid. If we can break this assumption, it would get rid of a lot of future pain.
