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Date:   Sun, 12 Nov 2017 12:45:10 -0800
From:   Ram Pai <linuxram@us.ibm.com>
To:     Christophe LEROY <christophe.leroy@c-s.fr>
Cc:     mpe@ellerman.id.au, mingo@redhat.com, akpm@linux-foundation.org,
        corbet@lwn.net, arnd@arndb.de, linux-arch@vger.kernel.org,
        ebiederm@xmission.com, linux-doc@vger.kernel.org, x86@kernel.org,
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        aneesh.kumar@linux.vnet.ibm.com, linux-kselftest@vger.kernel.org,
        bauerman@linux.vnet.ibm.com, linuxppc-dev@lists.ozlabs.org,
        khandual@linux.vnet.ibm.com
Subject: Re: [PATCH v9 00/51] powerpc, mm: Memory Protection Keys
Reply-To: Ram Pai <linuxram@us.ibm.com>
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On Fri, Nov 10, 2017 at 07:10:31PM +0100, Christophe LEROY wrote:
> Hi
> 
> Le 06/11/2017 � 09:56, Ram Pai a �crit�:
> >Memory protection keys enable applications to protect its
> >address space from inadvertent access from or corruption
> >by itself.
> >
> >These patches along with the pte-bit freeing patch series
> >enables the protection key feature on powerpc; 4k and 64k
> >hashpage kernels. It also changes the generic and x86
> >code to expose memkey features through sysfs. Finally
> >testcases and Documentation is updated.
> >
> >All patches can be found at --
> >https://github.com/rampai/memorykeys.git memkey.v9
> 
> As far as I can see you are focussing the implementation on 64 bits
> powerpc. This could also be implemented on 32 bits powerpc, for
> instance the 8xx has MMU Access Protection Registers which can be
> used to define 16 domains and could I think be used for implementing
> protection keys.

I was assuming non-existence of any 32bit powerpc
systems supporting memory keys. Sounds like it was a wrong assumption.

However, I think, the framework as it stands today should work. All
the functionality is captured in pkeys.c and pkeys.h which are generic
ppc files.  Its just a matter of providing the 32-bit implementation
for whichever sub-arch that support it.  Can you point me to problem
areas? I will fix them.

Thanks for you interest. Togather we should be able to make it
happen.


> Of course the challenge after that would be to find 4 spare PTE
> bits, I'm sure we can find them on the 8xx, at least when using 16k
> pages we have 2 bits already available, then by merging PAGE_SHARED
> and PAGE_USER and by reducing PAGE_RO to only one bit we can get the
> 4 spare bits.

yes. This needs to happen parallely.
RP

> 
> Therefore I think it would be great if you could implement a
> framework common to both PPC32 and PPC64.


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