Date: Wed, 12 Jul 2017 09:39:45 +0200
From: Michal Hocko <mhocko@kernel.org>
To: Ram Pai <linuxram@us.ibm.com>
Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        linux-arch@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org,
        linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org,
        benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au,
        khandual@linux.vnet.ibm.com, aneesh.kumar@linux.vnet.ibm.com,
        bsingharora@gmail.com, dave.hansen@intel.com, hbabu@us.ibm.com,
        arnd@arndb.de, akpm@linux-foundation.org, corbet@lwn.net,
        mingo@redhat.com
Subject: Re: [RFC v5 00/38] powerpc: Memory Protection Keys
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On Wed 12-07-17 09:23:37, Michal Hocko wrote:
> On Tue 11-07-17 12:32:57, Ram Pai wrote:
[...]
> > Ideally the MMU looks at the PTE for keys, in order to enforce
> > protection. This is the case with x86 and is the case with power9 Radix
> > page table. Hence the keys have to be programmed into the PTE.
> 
> But x86 doesn't update ptes for PKEYs, that would be just too expensive.
> You could use standard mprotect to do the same...

OK, this seems to be a misunderstanding and confusion on my end.
do_mprotect_pkey does mprotect_fixup even for the pkey path which is
quite surprising to me. I guess my misunderstanding comes from
Documentation/x86/protection-keys.txt
"
Memory Protection Keys provides a mechanism for enforcing page-based
protections, but without requiring modification of the page tables
when an application changes protection domains.  It works by
dedicating 4 previously ignored bits in each page table entry to a
"protection key", giving 16 possible keys.
"

So please disregard my previous comments about page tables and sorry
about the confusion.
-- 
Michal Hocko
SUSE Labs