powerpc/mm/slice: Allow up to 64 low slices

While the implementation of the "slices" address space allows
a significant amount of high slices, it limits the number of
low slices to 16 due to the use of a single u64 low_slices_psize
element in struct mm_context_t

On the 8xx, the minimum slice size is the size of the area
covered by a single PMD entry, ie 4M in 4K pages mode and 64M in
16K pages mode. This means we could have at least 64 slices.

In order to override this limitation, this patch switches the
handling of low_slices_psize to char array as done already for
high_slices_psize.
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

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

@@ -91,7 +91,8 @@ typedef struct {
 	struct npu_context *npu_context;
 
 #ifdef CONFIG_PPC_MM_SLICES
-	u64 low_slices_psize;	/* SLB page size encodings */
+	 /* SLB page size encodings*/
+	unsigned char low_slices_psize[BITS_PER_LONG / BITS_PER_BYTE];
 	unsigned char high_slices_psize[SLICE_ARRAY_SIZE];
 	unsigned long slb_addr_limit;
 #else

arch/powerpc/include/asm/mmu-8xx.h

@@ -186,6 +186,11 @@
 #define M_APG2		0x00000040
 #define M_APG3		0x00000060
 
+#ifdef CONFIG_PPC_MM_SLICES
+#include <asm/nohash/32/slice.h>
+#define SLICE_ARRAY_SIZE	(1 << (32 - SLICE_LOW_SHIFT - 1))
+#endif
+
 #ifndef __ASSEMBLY__
 typedef struct {
 	unsigned int id;
@@ -193,7 +198,7 @@ typedef struct {
 	unsigned long vdso_base;
 #ifdef CONFIG_PPC_MM_SLICES
 	u16 user_psize;		/* page size index */
-	u64 low_slices_psize;	/* page size encodings */
+	unsigned char low_slices_psize[SLICE_ARRAY_SIZE];
 	unsigned char high_slices_psize[0];
 	unsigned long slb_addr_limit;
 #endif

arch/powerpc/include/asm/paca.h

@@ -141,7 +141,7 @@ struct paca_struct {
 #ifdef CONFIG_PPC_BOOK3S
 	mm_context_id_t mm_ctx_id;
 #ifdef CONFIG_PPC_MM_SLICES
-	u64 mm_ctx_low_slices_psize;
+	unsigned char mm_ctx_low_slices_psize[BITS_PER_LONG / BITS_PER_BYTE];
 	unsigned char mm_ctx_high_slices_psize[SLICE_ARRAY_SIZE];
 	unsigned long mm_ctx_slb_addr_limit;
 #else

arch/powerpc/kernel/paca.c

@@ -265,7 +265,8 @@ void copy_mm_to_paca(struct mm_struct *mm)
 #ifdef CONFIG_PPC_MM_SLICES
 	VM_BUG_ON(!mm->context.slb_addr_limit);
 	get_paca()->mm_ctx_slb_addr_limit = mm->context.slb_addr_limit;
-	get_paca()->mm_ctx_low_slices_psize = context->low_slices_psize;
+	memcpy(&get_paca()->mm_ctx_low_slices_psize,
+	       &context->low_slices_psize, sizeof(context->low_slices_psize));
 	memcpy(&get_paca()->mm_ctx_high_slices_psize,
 	       &context->high_slices_psize, TASK_SLICE_ARRAY_SZ(mm));
 #else /* CONFIG_PPC_MM_SLICES */

arch/powerpc/mm/hash_utils_64.c

@@ -1110,19 +1110,18 @@ unsigned int hash_page_do_lazy_icache(unsigned int pp, pte_t pte, int trap)
 #ifdef CONFIG_PPC_MM_SLICES
 static unsigned int get_paca_psize(unsigned long addr)
 {
-	u64 lpsizes;
-	unsigned char *hpsizes;
+	unsigned char *psizes;
 	unsigned long index, mask_index;
 
 	if (addr < SLICE_LOW_TOP) {
-		lpsizes = get_paca()->mm_ctx_low_slices_psize;
+		psizes = get_paca()->mm_ctx_low_slices_psize;
 		index = GET_LOW_SLICE_INDEX(addr);
-		return (lpsizes >> (index * 4)) & 0xF;
+	} else {
+		psizes = get_paca()->mm_ctx_high_slices_psize;
+		index = GET_HIGH_SLICE_INDEX(addr);
 	}
-	hpsizes = get_paca()->mm_ctx_high_slices_psize;
-	index = GET_HIGH_SLICE_INDEX(addr);
 	mask_index = index & 0x1;
-	return (hpsizes[index >> 1] >> (mask_index * 4)) & 0xF;
+	return (psizes[index >> 1] >> (mask_index * 4)) & 0xF;
 }
 
 #else

arch/powerpc/mm/slb_low.S

@@ -200,10 +200,12 @@ END_MMU_FTR_SECTION_IFCLR(MMU_FTR_1T_SEGMENT)
 5:
 	/*
 	 * Handle lpsizes
-	 * r9 is get_paca()->context.low_slices_psize, r11 is index
+	 * r9 is get_paca()->context.low_slices_psize[index], r11 is mask_index
 	 */
-	ld	r9,PACALOWSLICESPSIZE(r13)
-	mr	r11,r10
+	srdi    r11,r10,1 /* index */
+	addi	r9,r11,PACALOWSLICESPSIZE
+	lbzx	r9,r13,r9		/* r9 is lpsizes[r11] */
+	rldicl	r11,r10,0,63		/* r11 = r10 & 0x1 */
 6:
 	sldi	r11,r11,2  /* index * 4 */
 	/* Extract the psize and multiply to get an array offset */

arch/powerpc/mm/slice.c

@@ -150,19 +150,21 @@ static void slice_mask_for_free(struct mm_struct *mm, struct slice_mask *ret,
 static void slice_mask_for_size(struct mm_struct *mm, int psize, struct slice_mask *ret,
 				unsigned long high_limit)
 {
-	unsigned char *hpsizes;
+	unsigned char *hpsizes, *lpsizes;
 	int index, mask_index;
 	unsigned long i;
-	u64 lpsizes;
 
 	ret->low_slices = 0;
 	if (SLICE_NUM_HIGH)
 		bitmap_zero(ret->high_slices, SLICE_NUM_HIGH);
 
 	lpsizes = mm->context.low_slices_psize;
-	for (i = 0; i < SLICE_NUM_LOW; i++)
-		if (((lpsizes >> (i * 4)) & 0xf) == psize)
+	for (i = 0; i < SLICE_NUM_LOW; i++) {
+		mask_index = i & 0x1;
+		index = i >> 1;
+		if (((lpsizes[index] >> (mask_index * 4)) & 0xf) == psize)
 			ret->low_slices |= 1u << i;
+	}
 
 	if (high_limit <= SLICE_LOW_TOP)
 		return;
@@ -218,8 +220,7 @@ static void slice_convert(struct mm_struct *mm, struct slice_mask mask, int psiz
 {
 	int index, mask_index;
 	/* Write the new slice psize bits */
-	unsigned char *hpsizes;
-	u64 lpsizes;
+	unsigned char *hpsizes, *lpsizes;
 	unsigned long i, flags;
 
 	slice_dbg("slice_convert(mm=%p, psize=%d)\n", mm, psize);
@@ -232,12 +233,13 @@ static void slice_convert(struct mm_struct *mm, struct slice_mask mask, int psiz
 
 	lpsizes = mm->context.low_slices_psize;
 	for (i = 0; i < SLICE_NUM_LOW; i++)
-		if (mask.low_slices & (1u << i))
-			lpsizes = (lpsizes & ~(0xful << (i * 4))) |
-				(((unsigned long)psize) << (i * 4));
-
-	/* Assign the value back */
-	mm->context.low_slices_psize = lpsizes;
+		if (mask.low_slices & (1u << i)) {
+			mask_index = i & 0x1;
+			index = i >> 1;
+			lpsizes[index] = (lpsizes[index] &
+					  ~(0xf << (mask_index * 4))) |
+				(((unsigned long)psize) << (mask_index * 4));
+		}
 
 	hpsizes = mm->context.high_slices_psize;
 	for (i = 0; i < GET_HIGH_SLICE_INDEX(mm->context.slb_addr_limit); i++) {
@@ -644,7 +646,7 @@ unsigned long arch_get_unmapped_area_topdown(struct file *filp,
 
 unsigned int get_slice_psize(struct mm_struct *mm, unsigned long addr)
 {
-	unsigned char *hpsizes;
+	unsigned char *psizes;
 	int index, mask_index;
 
 	/*
@@ -658,15 +660,14 @@ unsigned int get_slice_psize(struct mm_struct *mm, unsigned long addr)
 #endif
 	}
 	if (addr < SLICE_LOW_TOP) {
-		u64 lpsizes;
-		lpsizes = mm->context.low_slices_psize;
+		psizes = mm->context.low_slices_psize;
 		index = GET_LOW_SLICE_INDEX(addr);
-		return (lpsizes >> (index * 4)) & 0xf;
+	} else {
+		psizes = mm->context.high_slices_psize;
+		index = GET_HIGH_SLICE_INDEX(addr);
 	}
-	hpsizes = mm->context.high_slices_psize;
-	index = GET_HIGH_SLICE_INDEX(addr);
 	mask_index = index & 0x1;
-	return (hpsizes[index >> 1] >> (mask_index * 4)) & 0xf;
+	return (psizes[index >> 1] >> (mask_index * 4)) & 0xf;
 }
 EXPORT_SYMBOL_GPL(get_slice_psize);
 
@@ -687,8 +688,8 @@ EXPORT_SYMBOL_GPL(get_slice_psize);
 void slice_set_user_psize(struct mm_struct *mm, unsigned int psize)
 {
 	int index, mask_index;
-	unsigned char *hpsizes;
-	unsigned long flags, lpsizes;
+	unsigned char *hpsizes, *lpsizes;
+	unsigned long flags;
 	unsigned int old_psize;
 	int i;
 
@@ -706,12 +707,14 @@ void slice_set_user_psize(struct mm_struct *mm, unsigned int psize)
 	wmb();
 
 	lpsizes = mm->context.low_slices_psize;
-	for (i = 0; i < SLICE_NUM_LOW; i++)
-		if (((lpsizes >> (i * 4)) & 0xf) == old_psize)
-			lpsizes = (lpsizes & ~(0xful << (i * 4))) |
-				(((unsigned long)psize) << (i * 4));
-	/* Assign the value back */
-	mm->context.low_slices_psize = lpsizes;
+	for (i = 0; i < SLICE_NUM_LOW; i++) {
+		mask_index = i & 0x1;
+		index = i >> 1;
+		if (((lpsizes[index] >> (mask_index * 4)) & 0xf) == old_psize)
+			lpsizes[index] = (lpsizes[index] &
+					  ~(0xf << (mask_index * 4))) |
+				(((unsigned long)psize) << (mask_index * 4));
+	}
 
 	hpsizes = mm->context.high_slices_psize;
 	for (i = 0; i < SLICE_NUM_HIGH; i++) {