linux-kernel - Re: [PATCH] x86, powerpc : pkey-mprotect must allow pkey-0

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Date:   Fri, 9 Mar 2018 12:06:31 -0800
From:   Ram Pai <linuxram@...ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     mingo@...hat.com, akpm@...ux-foundation.org,
        linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org, x86@...nel.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        dave.hansen@...el.com, benh@...nel.crashing.org, paulus@...ba.org,
        khandual@...ux.vnet.ibm.com, aneesh.kumar@...ux.vnet.ibm.com,
        bsingharora@...il.com, hbabu@...ibm.com, mhocko@...nel.org,
        bauerman@...ux.vnet.ibm.com, ebiederm@...ssion.com, corbet@....net,
        arnd@...db.de, fweimer@...hat.com, msuchanek@...e.com,
        Ulrich.Weigand@...ibm.com
Subject: Re: [PATCH] x86, powerpc : pkey-mprotect must allow pkey-0

On Fri, Mar 09, 2018 at 09:19:53PM +1100, Michael Ellerman wrote:
> Ram Pai <linuxram@...ibm.com> writes:
> 
> > Once an address range is associated with an allocated pkey, it cannot be
> > reverted back to key-0. There is no valid reason for the above behavior.  On
> > the contrary applications need the ability to do so.
> 
> Please explain this in much more detail. Is it an ABI change?

Not necessarily an ABI change. older binary applications  will continue
to work. It can be considered as a bug-fix.

> 
> And why did we just notice this?

Yes. this was noticed by an application vendor.

> 
> > The patch relaxes the restriction.
> >
> > Tested on powerpc and x86_64.
> 
> Thanks, but please split the patch, one for each arch.

Will do.
RP