Re: [PATCH RFC] mm: add MAP_EXCLUSIVE to create exclusive user mappings

Florian Weimer
2019-10-28T20:23:26Z

* Mike Rapoport:

> On October 27, 2019 12:30:21 PM GMT+02:00, Florian Weimer
> <fw@deneb.enyo.de> wrote:
>>* Mike Rapoport:
>>
>>> The patch below aims to allow applications to create mappins that
>>have
>>> pages visible only to the owning process. Such mappings could be used
>>to
>>> store secrets so that these secrets are not visible neither to other
>>> processes nor to the kernel.
>>
>>How is this expected to interact with CRIU?
>
> CRIU dumps the memory contents using a parasite code from inside the
> dumpee address space, so it would work the same way as for the other
> mappings. Of course, at the restore time the exclusive mapping should
> be recreated with the appropriate flags.

Hmm, so it would use a bounce buffer to perform the extraction?

>>> I've only tested the basic functionality, the changes should be
>>verified
>>> against THP/migration/compaction. Yet, I'd appreciate early feedback.
>>
>>What are the expected semantics for VM migration? Should it fail?
>
> I don't quite follow. If qemu would use such mappings it would be able
> to transfer them during live migration.

I was wondering if the special state is supposed to bubble up to the
host eventually.