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Date: Tue, 8 May 2018 11:38:53 -0700
From: Ram Pai <linuxram@us.ibm.com>
To: Michal =?iso-8859-1?Q?Such=E1nek?= <msuchanek@suse.de>
Cc: fweimer@redhat.com, Dave Hansen <dave.hansen@intel.com>,
 Ingo Molnar <mingo@kernel.org>, mhocko@kernel.org,
 Ulrich.Weigand@de.ibm.com, paulus@samba.org,
 aneesh.kumar@linux.vnet.ibm.com, bauerman@linux.vnet.ibm.com,
 Thomas Gleixner <tglx@linutronix.de>, linuxppc-dev@lists.ozlabs.org,
 Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v3] powerpc, pkey: make protection key 0 less special
Reply-To: Ram Pai <linuxram@us.ibm.com>
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On Tue, May 08, 2018 at 07:03:36PM +0200, Michal Suchánek wrote:
> 
> How is the application denied setting the permissions on key 0 if it
> can program the register directly?

There is a UAMOR register. The userspace can change the permissions of a
given key; by modifying the bits in AMOR register, only if the kernel
has set the corresponding bit in the UAMOR register.  For key-0 the
kernel does not set the corresponding UAMOR bit.

RP