MIPS: Two-level pagetables for 64-bit kernels with 64KB pages.

For 64-bit kernels with 64KB pages and two level page tables, there are
42 bits worth of virtual address space This is larger than the 40 bits of
virtual address space obtained with the default 4KB Page size and three
levels, so there are no draw backs for using two level tables with this
configuration.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Cc: linux-mips@linux-mips.org
Patchwork: http://patchwork.linux-mips.org/patch/761/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/mm/init.c

@@ -477,7 +477,7 @@ unsigned long pgd_current[NR_CPUS];
  * will officially be retired.
  */
 pgd_t swapper_pg_dir[_PTRS_PER_PGD] __page_aligned(_PGD_ORDER);
-#ifdef CONFIG_64BIT
+#ifndef __PAGETABLE_PMD_FOLDED
 pmd_t invalid_pmd_table[PTRS_PER_PMD] __page_aligned(PMD_ORDER);
 #endif
 pte_t invalid_pte_table[PTRS_PER_PTE] __page_aligned(PTE_ORDER);

arch/mips/mm/pgtable-64.c

@@ -15,23 +15,31 @@
 void pgd_init(unsigned long page)
 {
 	unsigned long *p, *end;
+	unsigned long entry;
+
+#ifdef __PAGETABLE_PMD_FOLDED
+	entry = (unsigned long)invalid_pte_table;
+#else
+	entry = (unsigned long)invalid_pmd_table;
+#endif
 
  	p = (unsigned long *) page;
 	end = p + PTRS_PER_PGD;
 
 	while (p < end) {
-		p[0] = (unsigned long) invalid_pmd_table;
-		p[1] = (unsigned long) invalid_pmd_table;
-		p[2] = (unsigned long) invalid_pmd_table;
-		p[3] = (unsigned long) invalid_pmd_table;
-		p[4] = (unsigned long) invalid_pmd_table;
-		p[5] = (unsigned long) invalid_pmd_table;
-		p[6] = (unsigned long) invalid_pmd_table;
-		p[7] = (unsigned long) invalid_pmd_table;
+		p[0] = entry;
+		p[1] = entry;
+		p[2] = entry;
+		p[3] = entry;
+		p[4] = entry;
+		p[5] = entry;
+		p[6] = entry;
+		p[7] = entry;
 		p += 8;
 	}
 }
 
+#ifndef __PAGETABLE_PMD_FOLDED
 void pmd_init(unsigned long addr, unsigned long pagetable)
 {
 	unsigned long *p, *end;
@@ -40,17 +48,18 @@ void pmd_init(unsigned long addr, unsigned long pagetable)
 	end = p + PTRS_PER_PMD;
 
 	while (p < end) {
-		p[0] = (unsigned long)pagetable;
-		p[1] = (unsigned long)pagetable;
-		p[2] = (unsigned long)pagetable;
-		p[3] = (unsigned long)pagetable;
-		p[4] = (unsigned long)pagetable;
-		p[5] = (unsigned long)pagetable;
-		p[6] = (unsigned long)pagetable;
-		p[7] = (unsigned long)pagetable;
+		p[0] = pagetable;
+		p[1] = pagetable;
+		p[2] = pagetable;
+		p[3] = pagetable;
+		p[4] = pagetable;
+		p[5] = pagetable;
+		p[6] = pagetable;
+		p[7] = pagetable;
 		p += 8;
 	}
 }
+#endif
 
 void __init pagetable_init(void)
 {
@@ -59,8 +68,9 @@ void __init pagetable_init(void)
 
 	/* Initialize the entire pgd.  */
 	pgd_init((unsigned long)swapper_pg_dir);
+#ifndef __PAGETABLE_PMD_FOLDED
 	pmd_init((unsigned long)invalid_pmd_table, (unsigned long)invalid_pte_table);
-
+#endif
 	pgd_base = swapper_pg_dir;
 	/*
 	 * Fixed mappings:

arch/mips/mm/tlbex.c

@@ -549,11 +549,13 @@ build_get_pmde64(u32 **p, struct uasm_label **l, struct uasm_reloc **r,
 
 	uasm_i_andi(p, tmp, tmp, (PTRS_PER_PGD - 1)<<3);
 	uasm_i_daddu(p, ptr, ptr, tmp); /* add in pgd offset */
+#ifndef __PAGETABLE_PMD_FOLDED
 	uasm_i_dmfc0(p, tmp, C0_BADVADDR); /* get faulting address */
 	uasm_i_ld(p, ptr, 0, ptr); /* get pmd pointer */
 	uasm_i_dsrl(p, tmp, tmp, PMD_SHIFT-3); /* get pmd offset in bytes */
 	uasm_i_andi(p, tmp, tmp, (PTRS_PER_PMD - 1)<<3);
 	uasm_i_daddu(p, ptr, ptr, tmp); /* add in pmd offset */
+#endif
 }
 
 /*