linux-kernel - Re: [RFC v5 11/38] mm: introduce an additional vma bit for powerpc pkey

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Date:   Tue, 11 Jul 2017 11:10:46 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Ram Pai <linuxram@...ibm.com>, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-mm@...ck.org, x86@...nel.org, linux-doc@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Cc:     benh@...nel.crashing.org, paulus@...ba.org, mpe@...erman.id.au,
        khandual@...ux.vnet.ibm.com, aneesh.kumar@...ux.vnet.ibm.com,
        bsingharora@...il.com, hbabu@...ibm.com, arnd@...db.de,
        akpm@...ux-foundation.org, corbet@....net, mingo@...hat.com
Subject: Re: [RFC v5 11/38] mm: introduce an additional vma bit for powerpc
 pkey

On 07/05/2017 02:21 PM, Ram Pai wrote:
> Currently there are only 4bits in the vma flags to support 16 keys
> on x86.  powerpc supports 32 keys, which needs 5bits. This patch
> introduces an addition bit in the vma flags.
> 
> Signed-off-by: Ram Pai <linuxram@...ibm.com>
> ---
>  fs/proc/task_mmu.c |    6 +++++-
>  include/linux/mm.h |   18 +++++++++++++-----
>  2 files changed, 18 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index f0c8b33..2ddc298 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -666,12 +666,16 @@ static void show_smap_vma_flags(struct seq_file *m, struct vm_area_struct *vma)
>  		[ilog2(VM_MERGEABLE)]	= "mg",
>  		[ilog2(VM_UFFD_MISSING)]= "um",
>  		[ilog2(VM_UFFD_WP)]	= "uw",
> -#ifdef CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS
> +#ifdef CONFIG_ARCH_HAS_PKEYS
>  		/* These come out via ProtectionKey: */
>  		[ilog2(VM_PKEY_BIT0)]	= "",
>  		[ilog2(VM_PKEY_BIT1)]	= "",
>  		[ilog2(VM_PKEY_BIT2)]	= "",
>  		[ilog2(VM_PKEY_BIT3)]	= "",
> +#endif /* CONFIG_ARCH_HAS_PKEYS */
> +#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
> +		/* Additional bit in ProtectionKey: */
> +		[ilog2(VM_PKEY_BIT4)]	= "",
>  #endif

I'd probably just leave the #ifdef out and eat the byte or whatever of
storage that this costs us on x86.

>  	};
>  	size_t i;
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 7cb17c6..3d35bcc 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -208,21 +208,29 @@ extern int overcommit_kbytes_handler(struct ctl_table *, int, void __user *,
>  #define VM_HIGH_ARCH_BIT_1	33	/* bit only usable on 64-bit architectures */
>  #define VM_HIGH_ARCH_BIT_2	34	/* bit only usable on 64-bit architectures */
>  #define VM_HIGH_ARCH_BIT_3	35	/* bit only usable on 64-bit architectures */
> +#define VM_HIGH_ARCH_BIT_4	36	/* bit only usable on 64-bit arch */

Please just copy the above lines.

>  #define VM_HIGH_ARCH_0	BIT(VM_HIGH_ARCH_BIT_0)
>  #define VM_HIGH_ARCH_1	BIT(VM_HIGH_ARCH_BIT_1)
>  #define VM_HIGH_ARCH_2	BIT(VM_HIGH_ARCH_BIT_2)
>  #define VM_HIGH_ARCH_3	BIT(VM_HIGH_ARCH_BIT_3)
> +#define VM_HIGH_ARCH_4	BIT(VM_HIGH_ARCH_BIT_4)
>  #endif /* CONFIG_ARCH_USES_HIGH_VMA_FLAGS */
>  
> -#if defined(CONFIG_X86)
> -# define VM_PAT		VM_ARCH_1	/* PAT reserves whole VMA at once (x86) */
> -#if defined (CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS)
> +#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_BIT0	VM_HIGH_ARCH_0
>  # define VM_PKEY_BIT1	VM_HIGH_ARCH_1
>  # define VM_PKEY_BIT2	VM_HIGH_ARCH_2
>  # define VM_PKEY_BIT3	VM_HIGH_ARCH_3
> -#endif
> +#endif /* CONFIG_ARCH_HAS_PKEYS */

We have the space here, so can we just say that it's 4-bits on x86 and 5
on ppc?

> +#if defined(CONFIG_PPC64_MEMORY_PROTECTION_KEYS)
> +# define VM_PKEY_BIT4	VM_HIGH_ARCH_4 /* additional key bit used on ppc64 */
> +#endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */

Why bother #ifdef'ing a #define?

> +#if defined(CONFIG_X86)
> +# define VM_PAT		VM_ARCH_1	/* PAT reserves whole VMA at once (x86) */
>  #elif defined(CONFIG_PPC)
>  # define VM_SAO		VM_ARCH_1	/* Strong Access Ordering (powerpc) */
>  #elif defined(CONFIG_PARISC)
>