RE: [PATCH] x86/entry/64: randomize kernel stack offset upon syscall

[Reshetova, Elena]

> * Reshetova, Elena <elena.reshetova@xxxxxxxxx> wrote:
> 
> > CONFIG_PAGE_TABLE_ISOLATION=n:
> >
> > base:                                  Simple syscall: 0.0510 microseconds
> > get_random_bytes(4096 bytes buffer):   Simple syscall: 0.0597 microseconds
> >
> > So, pure speed wise get_random_bytes() with 1 page per-cpu buffer wins.
> 
> It still adds +17% overhead to the system call path, which is sad.
> Why is it so expensive?

I guess I can experiment further with buffer size increase and/or 
using HW acceleration (I mostly played around different rdrand paths now). 

What would be acceptable overheard approximately (so that I know how
much I need to squeeze this thing)? 

Best Regards,
Elena.