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Subject: Re: [PATCH] pkeys: Introduce PKEY_ALLOC_SIGNALINHERIT and change
 signal semantics
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From: Florian Weimer <fweimer@redhat.com>
Message-ID: <927c8325-4c98-d7af-b921-6aafcf8fe992@redhat.com>
Date: Mon, 7 May 2018 11:48:20 +0200
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To: Andy Lutomirski <luto@kernel.org>, linuxram@us.ibm.com
Cc: Dave Hansen <dave.hansen@intel.com>, Linux-MM <linux-mm@kvack.org>, Linux API <linux-api@vger.kernel.org>, linux-x86_64@vger.kernel.org, linux-arch <linux-arch@vger.kernel.org>, X86 ML <x86@kernel.org>, ".linuxppc-dev"@lists.ozlabs.org

On 05/03/2018 06:05 AM, Andy Lutomirski wrote:
> On Wed, May 2, 2018 at 7:11 PM Ram Pai <linuxram@us.ibm.com> wrote:
> 
>> On Wed, May 02, 2018 at 09:23:49PM +0000, Andy Lutomirski wrote:
>>>
>>>> If I recall correctly, the POWER maintainer did express a strong
> desire
>>>> back then for (what is, I believe) their current semantics, which my
>>>> PKEY_ALLOC_SIGNALINHERIT patch implements for x86, too.
>>>
>>> Ram, I really really don't like the POWER semantics.  Can you give some
>>> justification for them?  Does POWER at least have an atomic way for
>>> userspace to modify just the key it wants to modify or, even better,
>>> special load and store instructions to use alternate keys?
> 
>> I wouldn't call it POWER semantics. The way I implemented it on power
>> lead to the semantics, given that nothing was explicitly stated
>> about how the semantics should work within a signal handler.
> 
> I think that this is further evidence that we should introduce a new
> pkey_alloc() mode and deprecate the old.  To the extent possible, this
> thing should work the same way on x86 and POWER.

Do you propose to change POWER or to change x86?

Thanks,
Florian