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

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Date:   Wed, 20 Dec 2017 08:34:56 +1100
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Dave Hansen <dave.hansen@...el.com>, Ram Pai <linuxram@...ibm.com>
Cc:     mpe@...erman.id.au, mingo@...hat.com, akpm@...ux-foundation.org,
        corbet@....net, arnd@...db.de, linuxppc-dev@...ts.ozlabs.org,
        linux-mm@...ck.org, x86@...nel.org, linux-arch@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org, paulus@...ba.org,
        khandual@...ux.vnet.ibm.com, aneesh.kumar@...ux.vnet.ibm.com,
        bsingharora@...il.com, hbabu@...ibm.com, mhocko@...nel.org,
        bauerman@...ux.vnet.ibm.com, ebiederm@...ssion.com
Subject: Re: [PATCH v9 29/51] mm/mprotect, powerpc/mm/pkeys, x86/mm/pkeys:
 Add sysfs interface

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.

Ben.