Messages in this thread | | | From | David Hildenbrand <> | Subject | Re: [PATCH v17 07/10] mm: introduce memfd_secret system call to create "secret" memory areas | Date | Mon, 22 Feb 2021 10:38:10 +0100 |
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On 17.02.21 17:19, James Bottomley wrote: > On Tue, 2021-02-16 at 18:16 +0100, David Hildenbrand wrote: > [...] >>>> The discussion regarding migratability only really popped up >>>> because this is a user-visible thing and not being able to >>>> migrate can be a real problem (fragmentation, ZONE_MOVABLE, ...). >>> >>> I think the biggest use will potentially come from hardware >>> acceleration. If it becomes simple to add say encryption to a >>> secret page with no cost, then no flag needed. However, if we only >>> have a limited number of keys so once we run out no more encrypted >>> memory then it becomes a costly resource and users might want a >>> choice of being backed by encryption or not. >> >> Right. But wouldn't HW support with configurable keys etc. need more >> syscall parameters (meaning, even memefd_secret() as it is would not >> be sufficient?). I suspect the simplistic flag approach might not >> be sufficient. I might be wrong because I have no clue about MKTME >> and friends. > > The theory I was operating under is key management is automatic and > hidden, but key scarcity can't be, so if you flag requesting hardware > backing then you either get success (the kernel found a key) or failure > (the kernel is out of keys). If we actually want to specify the key > then we need an extra argument and we *must* have a new system call. > >> Anyhow, I still think extending memfd_create() might just be good >> enough - at least for now. > > I really think this is the wrong approach for a user space ABI. If we > think we'll ever need to move to a separate syscall, we should begin > with one. The pain of trying to shift userspace from memfd_create to a > new syscall would be enormous. It's not impossible (see clone3) but > it's a pain we should avoid if we know it's coming.
Sorry for the late reply, there is just too much going on :)
*If* we ever realize we need to pass more parameters we can easily have a new syscall for that purpose. *Then*, we know how that syscall will look like. Right now, it's just pure speculation.
Until then, going with memfd_create() works just fine IMHO.
The worst think that could happen is that we might not be able to create all fancy sectremem flavors in the future via memfd_create() but only via different, highly specialized syscall. I don't see a real problem with that.
-- Thanks,
David / dhildenb
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