linux-kernel - Re: [RFC v5 00/38] powerpc: Memory Protection Keys

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Message-ID: <20170712073945.GC28912@dhcp22.suse.cz>
Date:   Wed, 12 Jul 2017 09:39:45 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Ram Pai <linuxram@...ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
        linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org,
        benh@...nel.crashing.org, paulus@...ba.org, mpe@...erman.id.au,
        khandual@...ux.vnet.ibm.com, aneesh.kumar@...ux.vnet.ibm.com,
        bsingharora@...il.com, dave.hansen@...el.com, hbabu@...ibm.com,
        arnd@...db.de, akpm@...ux-foundation.org, corbet@....net,
        mingo@...hat.com
Subject: Re: [RFC v5 00/38] powerpc: Memory Protection Keys

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