On Mon, 2021-02-15 at 20:20 +0100, Michal Hocko wrote: [...] > > > What kind of flags are we talking about and why would that be a > > > problem with memfd_create interface? Could you be more specific > > > please? > > > > You mean what were the ioctl flags in the patch series linked > > above? They were SECRETMEM_EXCLUSIVE and SECRETMEM_UNCACHED in > > patch 3/5. > > OK I see. How many potential modes are we talking about? A few or > potentially many? Well I initially thought there were two (uncached or not) until you came up with the migratable or non-migratable, which affects the security properties. But now there's also potential for hardware backing, like mktme, described by flags as well. I suppose you could also use RDT to restrict which cache the data goes into: say L1 but not L2 on to lessen the impact of fully uncached (although the big thrust of uncached was to blunt hyperthread side channels). So there is potential for quite a large expansion even though I'd be willing to bet that a lot of the modes people have thought about turn out not to be very effective in the field. James
