Re: [PATCH 00/12] [RFC] x86: Memory Protection Keys

[Ingo Molnar <mingo@kernel.org>]

* Dave Hansen <dave@sr71.net> wrote:

> == FEATURE OVERVIEW ==
> 
> Memory Protection Keys for Userspace (PKU aka PKEYs) is a CPU 
> feature which will be found in future Intel CPUs.  The work here was 
> done with the aid of simulators.
> 
> Memory Protection Keys provides a mechanism for enforcing page-based 
> protections, but without requiring modification of the page tables 
> when an application changes protection domains.  It works by 
> dedicating 4 previously ignored bits in each page table entry to a 
> "protection key", giving 16 possible keys.
> 
> There is also a new user-accessible register (PKRU) with two 
> separate bits (Access Disable and Write Disable) for each key. Being 
> a CPU register, PKRU is inherently thread-local, potentially giving 
> each thread a different set of protections from every other thread.
> 
> There are two new instructions (RDPKRU/WRPKRU) for reading and 
> writing to the new register.  The feature is only available in 
> 64-bit mode, even though there is theoretically space in the PAE 
> PTEs.  These permissions are enforced on data access only and have 
> no effect on instruction fetches.

So I'm wondering what the primary usecases are for this feature?
Could you outline applications/workloads/libraries that would
benefit from this?

Thanks,

	Ingo