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 | Tue, 16 Feb 2021 18:16:36 +0100 |
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>> For the other parts, the question is what we actually want to let >> user space configure. >> >> Being able to specify "Very secure" "maximum secure" "average >> secure" all doesn't really make sense to me. > > Well, it doesn't to me either unless the user feels a cost/benefit, so > if max cost $100 per invocation and average cost nothing, most people > would chose average unless they had a very good reason not to. In your > migratable model, if we had separate limits for non-migratable and > migratable, with non-migratable being set low to prevent exhaustion, > max secure becomes a highly scarce resource, whereas average secure is > abundant then having the choice might make sense.
I hope that we can find a way to handle the migration part internally. Especially, because Mike wants the default to be "as secure as possible", so if there is a flag, it would have to be an opt-out flag.
I guess as long as we don't temporarily map it into the "owned" location in the direct map shared by all VCPUs we are in a good positon. But this needs more thought, of course.
> >> 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.
Anyhow, I still think extending memfd_create() might just be good enough - at least for now. Things like HW support might have requirements we don't even know yet and that we cannot even model in memfd_secret() right now.
-- Thanks,
David / dhildenb
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