powerpc: track allocation status of all pkeys

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.
Reviewed-by: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
Signed-off-by: Ram Pai <linuxram@us.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/book3s/64/mmu.h

@@ -108,6 +108,15 @@ typedef struct {
 #ifdef CONFIG_SPAPR_TCE_IOMMU
 	struct list_head iommu_group_mem_list;
 #endif
+
+#ifdef CONFIG_PPC_MEM_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;
 
 /*

arch/powerpc/include/asm/mmu_context.h

@@ -193,5 +193,9 @@ static inline bool arch_vma_access_permitted(struct vm_area_struct *vma,
 	return true;
 }
 
+#ifndef CONFIG_PPC_MEM_KEYS
+#define pkey_mm_init(mm)
+#endif /* CONFIG_PPC_MEM_KEYS */
+
 #endif /* __KERNEL__ */
 #endif /* __ASM_POWERPC_MMU_CONTEXT_H */

arch/powerpc/include/asm/pkeys.h

@@ -11,21 +11,94 @@
 #include <linux/jump_label.h>
 
 DECLARE_STATIC_KEY_TRUE(pkey_disabled);
-#define ARCH_VM_PKEY_FLAGS 0
+extern int pkeys_total; /* total pkeys as per device tree */
+extern u32 initial_allocation_mask; /* bits set for reserved keys */
+
+/*
+ * Define these here temporarily so we're not dependent on patching linux/mm.h.
+ * Once it's updated we can drop these.
+ */
+#ifndef VM_PKEY_BIT0
+# define VM_PKEY_SHIFT	VM_HIGH_ARCH_BIT_0
+# 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
+# define VM_PKEY_BIT4	VM_HIGH_ARCH_4
+#endif
+
+#define ARCH_VM_PKEY_FLAGS (VM_PKEY_BIT0 | VM_PKEY_BIT1 | VM_PKEY_BIT2 | \
+			    VM_PKEY_BIT3 | VM_PKEY_BIT4)
+
+#define arch_max_pkey() pkeys_total
+
+#define pkey_alloc_mask(pkey) (0x1 << pkey)
+
+#define mm_pkey_allocation_map(mm) (mm->context.pkey_allocation_map)
+
+#define __mm_pkey_allocated(mm, pkey) {	\
+	mm_pkey_allocation_map(mm) |= pkey_alloc_mask(pkey); \
+}
+
+#define __mm_pkey_free(mm, pkey) {	\
+	mm_pkey_allocation_map(mm) &= ~pkey_alloc_mask(pkey);	\
+}
+
+#define __mm_pkey_is_allocated(mm, pkey)	\
+	(mm_pkey_allocation_map(mm) & pkey_alloc_mask(pkey))
+
+#define __mm_pkey_is_reserved(pkey) (initial_allocation_mask & \
+				       pkey_alloc_mask(pkey))
 
 static inline bool mm_pkey_is_allocated(struct mm_struct *mm, int pkey)
 {
-	return false;
+	/* A reserved key is never considered as 'explicitly allocated' */
+	return ((pkey < arch_max_pkey()) &&
+		!__mm_pkey_is_reserved(pkey) &&
+		__mm_pkey_is_allocated(mm, pkey));
 }
 
+/*
+ * Returns a positive, 5-bit key on success, or -1 on failure.
+ * Relies on the mmap_sem to protect against concurrency in mm_pkey_alloc() and
+ * mm_pkey_free().
+ */
 static inline int mm_pkey_alloc(struct mm_struct *mm)
 {
+	/*
+	 * 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 (static_branch_likely(&pkey_disabled))
 		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_pkey_allocated(mm, ret);
+	return ret;
 }
 
 static inline int mm_pkey_free(struct mm_struct *mm, int pkey)
 {
+	if (static_branch_likely(&pkey_disabled))
+		return -1;
+
+	if (!mm_pkey_is_allocated(mm, pkey))
 		return -EINVAL;
+
+	__mm_pkey_free(mm, pkey);
+
+	return 0;
 }
 
 /*
@@ -48,4 +121,6 @@ static inline int arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
 {
 	return 0;
 }
+
+extern void pkey_mm_init(struct mm_struct *mm);
 #endif /*_ASM_POWERPC_KEYS_H */

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>
@@ -118,6 +119,7 @@ static int hash__init_new_context(struct mm_struct *mm)
 
 	subpage_prot_init_new_context(mm);
 
+	pkey_mm_init(mm);
 	return index;
 }
 

arch/powerpc/mm/pkeys.c

@@ -9,21 +9,61 @@
 
 DEFINE_STATIC_KEY_TRUE(pkey_disabled);
 bool pkey_execute_disable_supported;
+int  pkeys_total;		/* Total pkeys as per device tree */
+u32  initial_allocation_mask;	/* Bits set for reserved keys */
 
 int pkey_initialize(void)
 {
+	int os_reserved, i;
+
 	/*
 	 * Disable the pkey system till everything is in place. A subsequent
 	 * patch will enable it.
 	 */
 	static_branch_enable(&pkey_disabled);
 
+	/* Lets assume 32 keys */
+	pkeys_total = 32;
+
+	/*
+	 * Adjust the upper limit, based on the number of bits supported by
+	 * arch-neutral code.
+	 */
+	pkeys_total = min_t(int, pkeys_total,
+			(ARCH_VM_PKEY_FLAGS >> VM_PKEY_SHIFT));
+
 	/*
 	 * Disable execute_disable support for now. A subsequent patch will
 	 * enable it.
 	 */
 	pkey_execute_disable_supported = false;
+
+#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);
 	return 0;
 }
 
 arch_initcall(pkey_initialize);
+
+void pkey_mm_init(struct mm_struct *mm)
+{
+	if (static_branch_likely(&pkey_disabled))
+		return;
+	mm_pkey_allocation_map(mm) = initial_allocation_mask;
+}