[PATCH V2 00/13] powerpc/vas: Page fault handling for user space NX requests

[Haren Myneni]

On Mon, 2019-12-09 at 02:38 -0600, Segher Boessenkool wrote:
> Hi!
> 
> On Mon, Dec 09, 2019 at 06:37:09AM +0100, Christophe Leroy wrote:
> > What do you mean by NX ?
> 
> It is the Power9 "Nest Accelerator".  The patch series should ideally
> mention that right at the start, yeah.

Thanks, NX (Nest Accelerator) is introduced since power7+
(drivers/crypto/nx/)

Whereas on power9, VAS (Virtual Accelerator Switchboard) is introduced
which allows to open multiple channels to communicate with NX. kernel or
user space can interact with NX directly using copy/paste instructions.
Kernel support with NX-842 compression is already included in kernel. 

In the case of user space, NX can see page fault on the request buffer
and interrupts OS to handle this fault. This patch series adds page
fault handling in VAS for user space requests. 

I will repost this patch with more explanation on NX. 

> 
> > Up to now, NX has been standing for No-eXecute. That's a bit in segment 
> > registers on book3s/32 to forbid executing code.
> 
> That bit is called just N fwiw (and not really specific to 32-bit -- on
> 64-bit implementations it was part of segment table entries, and of SLB
> entries on newer machines).
> 
> 
> Segher