linux-kernel - Re: [RFC v2 03/12] powerpc: Implement sys_pkey_alloc and sys_pkey

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Message-ID: <874lvcuq6e.fsf@concordia.ellerman.id.au>
Date:   Mon, 19 Jun 2017 22:18:01 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Ram Pai <linuxram@...ibm.com>, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Cc:     benh@...nel.crashing.org, paulus@...ba.org,
        khandual@...ux.vnet.ibm.com, aneesh.kumar@...ux.vnet.ibm.com,
        bsingharora@...il.com, dave.hansen@...el.com, hbabu@...ibm.com,
        linuxram@...ibm.com
Subject: Re: [RFC v2 03/12] powerpc: Implement sys_pkey_alloc and sys_pkey_free system call.

Hi Ram,

Ram Pai <linuxram@...ibm.com> writes:
> Sys_pkey_alloc() allocates and returns available pkey
> Sys_pkey_free()  frees up the pkey.
>
> Total 32 keys are supported on powerpc. However pkey 0,1 and 31
> are reserved. So effectively we have 29 pkeys.
>
> Signed-off-by: Ram Pai <linuxram@...ibm.com>
> ---
>  include/linux/mm.h                           |  31 ++++---
>  include/uapi/asm-generic/mman-common.h       |   2 +-

Those changes need to be split out and acked by mm folks.

> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 7cb17c6..34ddac7 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -204,26 +204,35 @@ extern int overcommit_kbytes_handler(struct ctl_table *, int, void __user *,
>  #define VM_MERGEABLE	0x80000000	/* KSM may merge identical pages */
>  
>  #ifdef CONFIG_ARCH_USES_HIGH_VMA_FLAGS
> -#define VM_HIGH_ARCH_BIT_0	32	/* bit only usable on 64-bit architectures */
> -#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_0	32	/* bit only usable on 64-bit arch */
> +#define VM_HIGH_ARCH_BIT_1	33	/* bit only usable on 64-bit arch */
> +#define VM_HIGH_ARCH_BIT_2	34	/* bit only usable on 64-bit arch */
> +#define VM_HIGH_ARCH_BIT_3	35	/* bit only usable on 64-bit arch */

Please don't change the comments, it makes the diff harder to read.

You're actually just adding this AFAICS:

> +#define VM_HIGH_ARCH_BIT_4	36	/* bit only usable on 64-bit arch */

>  #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)
> -# 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_BIT2	VM_HIGH_ARCH_2
> -# define VM_PKEY_BIT3	VM_HIGH_ARCH_3
> -#endif
> +#if defined(CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS) \
> +	|| defined(CONFIG_PPC64_MEMORY_PROTECTION_KEYS)
> +#define VM_PKEY_SHIFT	VM_HIGH_ARCH_BIT_0
> +#define VM_PKEY_BIT0	VM_HIGH_ARCH_0	/* A protection key is a 5-bit value */
                                                                 ^ 4?
> +#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 /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */

That appears to be inside an #if defined(CONFIG_X86) ?

>  #elif defined(CONFIG_PPC)
                 ^
Should be CONFIG_PPC64_MEMORY_PROTECTION_KEYS no?

> +#define VM_PKEY_BIT0	VM_HIGH_ARCH_0	/* A protection key is a 5-bit value */
> +#define VM_PKEY_BIT1	VM_HIGH_ARCH_1
> +#define VM_PKEY_BIT2	VM_HIGH_ARCH_2
> +#define VM_PKEY_BIT3	VM_HIGH_ARCH_3
> +#define VM_PKEY_BIT4	VM_HIGH_ARCH_4  /* intel does not use this bit */
> +					/* but reserved for future expansion */

But this hunk is for PPC ?

Is it OK for the other arches & generic code to add another VM_PKEY_BIT4 ?

Do you need to update show_smap_vma_flags() ?

>  # define VM_SAO		VM_ARCH_1	/* Strong Access Ordering (powerpc) */
>  #elif defined(CONFIG_PARISC)
>  # define VM_GROWSUP	VM_ARCH_1

> diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
> index 8c27db0..b13ecc6 100644
> --- a/include/uapi/asm-generic/mman-common.h
> +++ b/include/uapi/asm-generic/mman-common.h
> @@ -76,5 +76,5 @@
>  #define PKEY_DISABLE_WRITE	0x2
>  #define PKEY_ACCESS_MASK	(PKEY_DISABLE_ACCESS |\
>  				 PKEY_DISABLE_WRITE)
> -
> +#define PKEY_DISABLE_EXECUTE	0x4

How you can set that if it's not in PKEY_ACCESS_MASK?

See:

SYSCALL_DEFINE2(pkey_alloc, unsigned long, flags, unsigned long, init_val)
{
	int pkey;
	int ret;

	/* No flags supported yet. */
	if (flags)
		return -EINVAL;
	/* check for unsupported init values */
	if (init_val & ~PKEY_ACCESS_MASK)
		return -EINVAL;


cheers