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

From: Dave Hansen <[email-masked]>
Date: Mon, 26 Feb 2018 13:14:34 -0800

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.