linux-kernel - Re: [PATCH v12 2/3] mm, powerpc, x86: introduce an additional vma bit for powerpc pkey

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Date:   Mon, 26 Feb 2018 13:14:34 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Ram Pai <linuxram@...ibm.com>, mpe@...erman.id.au,
        mingo@...hat.com, akpm@...ux-foundation.org
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-mm@...ck.org, x86@...nel.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.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
Subject: Re: [PATCH v12 2/3] mm, powerpc, x86: introduce an additional vma bit
 for powerpc pkey

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.