Subject: [RFC v7 02/25] powerpc: track allocation status of all pkeys

From: Ram Pai <[email-masked]>
Date: Sun, 30 Jul 2017 17:12:03 -0700

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.

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 <[email-masked]>
---
 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))
 
 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.
+ */
 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 */
-- 
1.7.1