linux-kernel - Re: [PATCH v3] x86: treat pkey-0 special

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Message-ID: <2bf8e659-5a8d-a2d5-ea52-e4d395ea2201@intel.com>
Date:   Thu, 15 Mar 2018 10:31:51 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Ram Pai <linuxram@...ibm.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>, mingo@...hat.com,
        mpe@...erman.id.au, linuxppc-dev@...ts.ozlabs.org,
        linux-mm@...ck.org, x86@...nel.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        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 v3] x86: treat pkey-0 special

On 03/15/2018 10:21 AM, Ram Pai wrote:
> On Thu, Mar 15, 2018 at 08:55:31AM -0700, Dave Hansen wrote:
>> On 03/15/2018 02:46 AM, Thomas Gleixner wrote:
>>>> +	if (!pkey || !mm_pkey_is_allocated(mm, pkey))
>>> Why this extra check? mm_pkey_is_allocated(mm, 0) should not return true
>>> ever. If it does, then this wants to be fixed.
>> I was thinking that we _do_ actually want it to seem allocated.  It just
>> get "allocated" implicitly when an mm is created.  I think that will
>> simplify the code if we avoid treating it specially in as many places as
>> possible.
> I think, the logic that makes pkey-0 special must to go
> in arch-neutral code.   How about checking for pkey-0 in sys_pkey_free()
> itself?

This is for protection against shooting yourself in the foot?  Yes, that
can go in sys_pkey_free().

Does this need manpage and/or selftests updates?