Hi Ram,
On 31/07/2017 02:12, Ram Pai wrote:
> Total 32 keys are available on power7 and above. However
> pkey 0,1 are reserved. So effectively we have 30 pkeys.
>
> On 4K kernels, we do not have 5 bits in the PTE to
> represent all the keys; we only have 3bits.Two of those
> keys are reserved; pkey 0 and pkey 1. So effectively we
> have 6 pkeys.
IIUC, the pkey 0 and 1 are reserved by the hardware, and the kernel PTE has
only 5 bits to keep track of the pkey. Why hw pkey 0 and 1 has to be
represented in the kernel PTE ?
> This patch keeps track of reserved keys, allocated keys
> and keys that are currently free.
>
> Also it adds skeletal functions and macros, that the
> architecture-independent code expects to be available.
>
> Signed-off-by: Ram Pai <linux...@us.ibm.com>
> ---
> arch/powerpc/include/asm/book3s/64/mmu.h | 9 +++
> arch/powerpc/include/asm/mmu_context.h | 1 +
> arch/powerpc/include/asm/pkeys.h | 98 ++++++++++++++++++++++++++++-
> arch/powerpc/mm/mmu_context_book3s64.c | 2 +
> arch/powerpc/mm/pkeys.c | 2 +
> 5 files changed, 108 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/book3s/64/mmu.h
> b/arch/powerpc/include/asm/book3s/64/mmu.h
> index 77529a3..104ad72 100644
> --- a/arch/powerpc/include/asm/book3s/64/mmu.h
> +++ b/arch/powerpc/include/asm/book3s/64/mmu.h
> @@ -108,6 +108,15 @@ struct patb_entry {
> #ifdef CONFIG_SPAPR_TCE_IOMMU
> struct list_head iommu_group_mem_list;
> #endif
> +
> +#ifdef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
> + /*
> + * Each bit represents one protection key.
> + * bit set -> key allocated
> + * bit unset -> key available for allocation
> + */
> + u32 pkey_allocation_map;
> +#endif
> } mm_context_t;
>
> /*
> diff --git a/arch/powerpc/include/asm/mmu_context.h
> b/arch/powerpc/include/asm/mmu_context.h
> index 4b93547..4705dab 100644
> --- a/arch/powerpc/include/asm/mmu_context.h
> +++ b/arch/powerpc/include/asm/mmu_context.h
> @@ -184,6 +184,7 @@ static inline bool arch_vma_access_permitted(struct
> vm_area_struct *vma,
>
> #ifndef CONFIG_PPC64_MEMORY_PROTECTION_KEYS
> #define pkey_initialize()
> +#define pkey_mm_init(mm)
> #endif /* CONFIG_PPC64_MEMORY_PROTECTION_KEYS */
>
> #endif /* __KERNEL__ */
> diff --git a/arch/powerpc/include/asm/pkeys.h
> b/arch/powerpc/include/asm/pkeys.h
> index 4ccb8f5..def385f 100644
> --- a/arch/powerpc/include/asm/pkeys.h
> +++ b/arch/powerpc/include/asm/pkeys.h
> @@ -2,6 +2,8 @@
> #define _ASM_PPC64_PKEYS_H
>
> extern bool pkey_inited;
> +extern int pkeys_total; /* total pkeys as per device tree */
> +extern u32 initial_allocation_mask;/* bits set for reserved keys */
>
> /*
> * powerpc needs an additional vma bit to support 32 keys.
> @@ -20,21 +22,76 @@
> #define VM_PKEY_BIT4 VM_HIGH_ARCH_4
> #endif
>
> -#define ARCH_VM_PKEY_FLAGS 0
> +#define arch_max_pkey() pkeys_total
> +#define ARCH_VM_PKEY_FLAGS (VM_PKEY_BIT0 | VM_PKEY_BIT1 | VM_PKEY_BIT2 | \
> + VM_PKEY_BIT3 | VM_PKEY_BIT4)
> +
> +#define pkey_alloc_mask(pkey) (0x1 << pkey)
> +
> +#define mm_pkey_allocation_map(mm) (mm->context.pkey_allocation_map)
> +
> +#define mm_set_pkey_allocated(mm, pkey) { \
> + mm_pkey_allocation_map(mm) |= pkey_alloc_mask(pkey); \
> +}
> +
> +#define mm_set_pkey_free(mm, pkey) { \
> + mm_pkey_allocation_map(mm) &= ~pkey_alloc_mask(pkey); \
> +}
> +
> +#define mm_set_pkey_is_allocated(mm, pkey) \
> + (mm_pkey_allocation_map(mm) & pkey_alloc_mask(pkey))
> +
> +#define mm_set_pkey_is_reserved(mm, pkey) (initial_allocation_mask & \
> + pkey_alloc_mask(pkey))
This macro doesn't need a 'mm' argument.
> static inline bool mm_pkey_is_allocated(struct mm_struct *mm, int pkey)
> {
> - return (pkey == 0);
> + /* a reserved key is never considered as 'explicitly allocated' */
> + return ((pkey < arch_max_pkey()) &&
> + !mm_set_pkey_is_reserved(mm, pkey) &&
> + mm_set_pkey_is_allocated(mm, pkey));
> }
>
> +/*
> + * Returns a positive, 5-bit key on success, or -1 on failure.
I guess you rely on the mmap_sem to protect against concurrency in
mm_pkey_alloc() and mm_pkey_free().
As this is not explicit in the code, it should at least be mentioned in the
comment describing the function.
> + */
> static inline int mm_pkey_alloc(struct mm_struct *mm)
> {
> - return -1;
> + /*
> + * Note: this is the one and only place we make sure
> + * that the pkey is valid as far as the hardware is
> + * concerned. The rest of the kernel trusts that
> + * only good, valid pkeys come out of here.
> + */
> + u32 all_pkeys_mask = (u32)(~(0x0));
> + int ret;
> +
> + if (!pkey_inited)
> + return -1;
> + /*
> + * Are we out of pkeys? We must handle this specially
> + * because ffz() behavior is undefined if there are no
> + * zeros.
> + */
> + if (mm_pkey_allocation_map(mm) == all_pkeys_mask)
> + return -1;
> +
> + ret = ffz((u32)mm_pkey_allocation_map(mm));
> + mm_set_pkey_allocated(mm, ret);
> + return ret;
> }
>
> static inline int mm_pkey_free(struct mm_struct *mm, int pkey)
> {
> - return -EINVAL;
> + if (!pkey_inited)
> + return -1;
> +
> + if (!mm_pkey_is_allocated(mm, pkey))
> + return -EINVAL;
> +
> + mm_set_pkey_free(mm, pkey);
> +
> + return 0;
> }
>
> /*
> @@ -58,12 +115,45 @@ static inline int arch_set_user_pkey_access(struct
> task_struct *tsk, int pkey,
> return 0;
> }
>
> +static inline void pkey_mm_init(struct mm_struct *mm)
> +{
> + if (!pkey_inited)
> + return;
> + mm_pkey_allocation_map(mm) = initial_allocation_mask;
> +}
> +
> static inline void pkey_initialize(void)
> {
> + int os_reserved, i;
> +
> /* disable the pkey system till everything
> * is in place. A patch further down the
> * line will enable it.
> */
> pkey_inited = false;
> +
> + /* Lets assume 32 keys */
> + pkeys_total = 32;
> +
> +#ifdef CONFIG_PPC_4K_PAGES
> + /*
> + * the OS can manage only 8 pkeys
> + * due to its inability to represent
> + * them in the linux 4K-PTE.
> + */
> + os_reserved = pkeys_total-8;
> +#else
> + os_reserved = 0;
> +#endif
> + /*
> + * Bits are in LE format.
> + * NOTE: 1, 0 are reserved.
> + * key 0 is the default key, which allows read/write/execute.
> + * key 1 is recommended not to be used.
> + * PowerISA(3.0) page 1015, programming note.
> + */
> + initial_allocation_mask = ~0x0;
> + for (i = 2; i < (pkeys_total - os_reserved); i++)
> + initial_allocation_mask &= ~(0x1<<i);
> }
> #endif /*_ASM_PPC64_PKEYS_H */
> diff --git a/arch/powerpc/mm/mmu_context_book3s64.c
> b/arch/powerpc/mm/mmu_context_book3s64.c
> index a3edf81..34a16f3 100644
> --- a/arch/powerpc/mm/mmu_context_book3s64.c
> +++ b/arch/powerpc/mm/mmu_context_book3s64.c
> @@ -16,6 +16,7 @@
> #include <linux/string.h>
> #include <linux/types.h>
> #include <linux/mm.h>
> +#include <linux/pkeys.h>
> #include <linux/spinlock.h>
> #include <linux/idr.h>
> #include <linux/export.h>
> @@ -120,6 +121,7 @@ static int hash__init_new_context(struct mm_struct *mm)
>
> subpage_prot_init_new_context(mm);
>
> + pkey_mm_init(mm);
> return index;
> }
>
> diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
> index c3acee1..37dacc5 100644
> --- a/arch/powerpc/mm/pkeys.c
> +++ b/arch/powerpc/mm/pkeys.c
> @@ -16,3 +16,5 @@
> #include <linux/pkeys.h> /* PKEY_* */
>
> bool pkey_inited;
> +int pkeys_total; /* total pkeys as per device tree */
> +u32 initial_allocation_mask; /* bits set for reserved keys */
>
