On Mon, 2016-10-03 at 14:36 -0700, Andy Lutomirski wrote: > > Anything else that tries to read task xstate from memory, i.e. MPX > and > PKRU. (Although if we switch to eager-switched PKRU, then PKRU stops > mattering for this purpose.) > > Actually, I don't see any way your patches can be compatible with > PKRU > without switching to eager-switched PKRU.
There is one case where the in-register PKRU state matters: - user space accesses to memory There are several cases where the in-memory PKRU state would suffice: - get_user_pages(_fast) to the local task (could also use registers) - setting VMA/PTE permission bits (could also use registers) There is one case where only in-memory PKRU state works, where PKRU is currently simply ignored: - get_user_pages to another task's memory Dave, are there major obstacles to making read_pkru and write_pkru work with in-memory state? Would it be better for read/write_pkru to force the FPU state to get loaded into registers, under the assumption that if things like get_user_pages_fast happens, we will likely switch back to userspace soon, anyway? Would that assumption be wrong with KVM? :) -- All Rights Reversed.
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