Re: [PATCH v9 29/51] mm/mprotect, powerpc/mm/pkeys, x86/mm/pkeys: Add sysfs interface

From: Benjamin Herrenschmidt
Date: Tue Dec 19 2017 - 16:36:01 EST

On Mon, 2017-12-18 at 14:28 -0800, Dave Hansen wrote:
> > We do not have generic support for something like that on ppc.
> > The kernel looks at the device tree to determine what hardware features
> > are available. But does not have mechanism to tell the hardware to track
> > which of its features are currently enabled/used by the kernel; atleast
> > not for the memory-key feature.
> Bummer. You're missing out.
> But, you could still do this with a syscall. "Hey, kernel, do you
> support this feature?"

I'm not sure I understand Ram's original (quoted) point, but informing
userspace of CPU features is what AT_HWCAP's are about.