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Subject: Re: [PATCH v12 2/3] mm, powerpc, x86: introduce an additional vma bit
 for powerpc pkey
To:     Ram Pai <linuxram@us.ibm.com>, mpe@ellerman.id.au,
        mingo@redhat.com, akpm@linux-foundation.org
References: <1519257138-23797-1-git-send-email-linuxram@us.ibm.com>
 <1519257138-23797-3-git-send-email-linuxram@us.ibm.com>
Cc:     linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, x86@kernel.org,
        linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
        benh@kernel.crashing.org, paulus@samba.org,
        khandual@linux.vnet.ibm.com, aneesh.kumar@linux.vnet.ibm.com,
        bsingharora@gmail.com, hbabu@us.ibm.com, mhocko@kernel.org,
        bauerman@linux.vnet.ibm.com, ebiederm@xmission.com, corbet@lwn.net,
        arnd@arndb.de, fweimer@redhat.com, msuchanek@suse.com
From:   Dave Hansen <dave.hansen@intel.com>
Message-ID: <d3f6b6a1-8319-449a-804e-bf9d1dedbb5f@intel.com>
Date:   Mon, 26 Feb 2018 13:14:34 -0800
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On 02/21/2018 03:52 PM, Ram Pai wrote:
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index ad207ad..d534f46 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -231,9 +231,10 @@ extern int overcommit_kbytes_handler(struct ctl_table *, int, void __user *,
>  #ifdef CONFIG_ARCH_HAS_PKEYS
>  # define VM_PKEY_SHIFT	VM_HIGH_ARCH_BIT_0
>  # define VM_PKEY_BIT0	VM_HIGH_ARCH_0	/* A protection key is a 4-bit value */
> -# define VM_PKEY_BIT1	VM_HIGH_ARCH_1
> +# define VM_PKEY_BIT1	VM_HIGH_ARCH_1	/* on x86 and 5-bit value on ppc64   */
>  # define VM_PKEY_BIT2	VM_HIGH_ARCH_2
>  # define VM_PKEY_BIT3	VM_HIGH_ARCH_3
> +# define VM_PKEY_BIT4	VM_HIGH_ARCH_4
>  #endif /* CONFIG_ARCH_HAS_PKEYS */

I think I would prefer if VM_PKEY_BIT4 was unusable on x86, or #defined
to 0.  We don't want folks using a bit that can not be programmed into
the hardware.