Messages in this thread | | | Subject | Re: [PATCH 6/9] x86, pkeys: add pkey set/get syscalls | From | Dave Hansen <> | Date | Tue, 12 Jul 2016 08:39:07 -0700 |
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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.
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