On 07/12/2016 12:13 AM, Ingo Molnar wrote: >> > Remember, PKRU is just a *bitmap*. The only place keys are stored is in the >> > page tables. > A pkey is an index *and* a protection mask. So by representing it as a bitmask we > lose per thread information. This is what I meant by 'incomplete shadowing' - for > example the debug code couldn't work: if we cleared a pkey in a task we wouldn't > know what to restore it to with the current data structures, right? Right. I actually have some code to do the shadowing that I wrote to explore how to do different PKRU values in signal handlers. The code only shadowed the keys that were currently allocated, and used the (mm-wide) allocation map to figure that out. It did not have a separate per-thread concept of which parts of PKRU need to be shadowed. It essentially populated the shadow value on all pkru_set() calls. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>