Re: [RFC PATCH] mm: extend memfd with ability to create "secret" memory areas

Dave Hansen
2020-02-06T18:51:15Z

On 1/30/20 8:23 AM, Mike Rapoport wrote:
> include/linux/memfd.h | 9 ++
> include/uapi/linux/magic.h | 1 +
> include/uapi/linux/memfd.h | 6 +
> mm/Kconfig | 4 +
> mm/Makefile | 1 +
> mm/memfd.c | 10 +-
> mm/secretmem.c | 244 +++++++++++++++++++++++++++++++++++++
> 7 files changed, 273 insertions(+), 2 deletions(-)

It seems pretty self-contained and relatively harmless.

But, how much work is it going to be to tell the rest of the kernel that
page_to_virt() doesn't work any more? Do we need to make kmap() work on
these?

I guess fixing vm_normal_page() would fix a lot of that.

In general, my concern about creating little self-contained memory types
is that they will get popular and folks will start wanting more features
from them. For instance, what if I want NUMA affinity, migration, or
large page mappings that are secret?

Can these pages work as guest memory?

Who would the first users of this thing be?