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>

2 files changed, 42 insertions, 0 deletions

diff --git a/arch/powerpc/mm/mmu_context_book3s64.c b/arch/powerpc/mm/mmu_context_book3s64.c
index 59c0766ae4e0..929d9ef7083f 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>
@@ -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;
 }
 
diff --git a/arch/powerpc/mm/pkeys.c b/arch/powerpc/mm/pkeys.c
index a11afba584b9..e68e367dcdd7 100644
--- a/arch/powerpc/mm/pkeys.c
+++ b/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;
+}