[LSF/MM/BPF TOPIC] PKS for the page cache and beyond

[Ira Weiny <ira.weiny@intel.com>]

Resend due to typo in tag. s/PPF/BPF/

However, I also realized one should fill out the google form now.  I'll do that
straight away.

Thanks,
Ira

On Fri, Feb 25, 2022 at 08:10:30AM -0800, Ira Weiny wrote:
> Hello,
> 
> Protection Key Supervisor (PKS) presents a way to control access to a large
> domain of memory quickly, without a page table walk or TLB flush, as well as
> with finer granularity; allowing protection control on individual threads.
> 
> Multiple areas of memory have been identified as candidates to be protected
> with PKS.  These include the initial use case persistent memory (PMEM), page
> tables[1], kernel secret keys[2], and the page cache.[3]  Like PMEM the page
> cache presents a significant surface area where stray writes, or other bugs,
> could corrupt data permanently.
> 
> I would like to discuss the ramifications of being able to change memory
> permissions in this new way.  While PKS has a lot to offer it does not come for
> free.  One trade off is the loss of direct access via page_address() in
> !HIGHMEM builds.
> 
> Already PMEM's faced challenges in the leverage of kmap/kunmap.  While the page
> cache should be able to leverage this work, this is driving a redefinition of
> what kmap means.  Especially since the HIGHMEM use case is increasingly
> meaningless on modern machines.
> 
> Ira Weiny
> 
> [1] https://lore.kernel.org/lkml/20210830235927.6443-2-rick.p.edgecombe@intel.com/
> [2] https://lore.kernel.org/lkml/20201009201410.3209180-3-ira.weiny@intel.com/
> [3] https://lwn.net/Articles/883352/