Message-ID: <1513719296.2743.12.camel@kernel.crashing.org>
Subject: Re: [PATCH v9 29/51] mm/mprotect, powerpc/mm/pkeys, x86/mm/pkeys:
 Add sysfs interface
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Dave Hansen <dave.hansen@intel.com>, Ram Pai <linuxram@us.ibm.com>
Cc: mpe@ellerman.id.au, mingo@redhat.com, akpm@linux-foundation.org,
        corbet@lwn.net, arnd@arndb.de, linuxppc-dev@lists.ozlabs.org,
        linux-mm@kvack.org, x86@kernel.org, linux-arch@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org,
        linux-kernel@vger.kernel.org, paulus@samba.org,
        khandual@linux.vnet.ibm.com, aneesh.kumar@linux.vnet.ibm.com,
        bsingharora@gmail.com, hbabu@us.ibm.com, mhocko@kernel.org,
        bauerman@linux.vnet.ibm.com, ebiederm@xmission.com
Date: Wed, 20 Dec 2017 08:34:56 +1100
In-Reply-To: <e7971d03-6ad1-40d5-9b79-f01242db5293@intel.com>
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         <bbc5593e-31ec-183a-01a5-1a253dc0c275@intel.com>
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         <e7971d03-6ad1-40d5-9b79-f01242db5293@intel.com>
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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.