m68k: mm: Restructure Motorola MMU page-table layout

The Motorola 68xxx MMUs, 040 (and later) have a fixed 7,7,{5,6}
page-table setup, where the last depends on the page-size selected (8k
vs 4k resp.), and head.S selects 4K pages. For 030 (and earlier) we
explicitly program 7,7,6 and 4K pages in %tc.

However, the current code implements this mightily weird. What it does
is group 16 of those (6 bit) pte tables into one 4k page to not waste
space. The down-side is that that forces pmd_t to be a 16-tuple
pointing to consecutive pte tables.

This breaks the generic code which assumes READ_ONCE(*pmd) will be
word sized.

Therefore implement a straight forward 7,7,6 3 level page-table setup,
with the addition (for 020/030) of (partial) large-page support. For
now this increases the memory footprint for pte-tables 15 fold.

Tested with ARAnyM/68040 emulation.

Suggested-by: Will Deacon <will@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Greg Ungerer <gerg@linux-m68k.org>
Tested-by: Michael Schmitz <schmitzmic@gmail.com>
Tested-by: Greg Ungerer <gerg@linux-m68k.org>
Link: https://lore.kernel.org/r/20200131125403.711478295@infradead.org
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

3 files changed, 10 insertions, 21 deletions

diff --git a/arch/m68k/include/asm/motorola_pgtable.h b/arch/m68k/include/asm/motorola_pgtable.h
index 62bedc61f110..4d94e462bb2b 100644
--- a/arch/m68k/include/asm/motorola_pgtable.h
+++ b/arch/m68k/include/asm/motorola_pgtable.h
@@ -108,13 +108,7 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
 
 static inline void pmd_set(pmd_t *pmdp, pte_t *ptep)
 {
-	unsigned long ptbl = virt_to_phys(ptep) | _PAGE_TABLE | _PAGE_ACCESSED;
-	unsigned long *ptr = pmdp->pmd;
-	short i = 16;
-	while (--i >= 0) {
-		*ptr++ = ptbl;
-		ptbl += (sizeof(pte_t)*PTRS_PER_PTE/16);
-	}
+	pmd_val(*pmdp) = virt_to_phys(ptep) | _PAGE_TABLE | _PAGE_ACCESSED;
 }
 
 static inline void pud_set(pud_t *pudp, pmd_t *pmdp)
@@ -138,12 +132,7 @@ static inline void pud_set(pud_t *pudp, pmd_t *pmdp)
 #define pmd_none(pmd)		(!pmd_val(pmd))
 #define pmd_bad(pmd)		((pmd_val(pmd) & _DESCTYPE_MASK) != _PAGE_TABLE)
 #define pmd_present(pmd)	(pmd_val(pmd) & _PAGE_TABLE)
-#define pmd_clear(pmdp) ({			\
-	unsigned long *__ptr = pmdp->pmd;	\
-	short __i = 16;				\
-	while (--__i >= 0)			\
-		*__ptr++ = 0;			\
-})
+#define pmd_clear(pmdp)		({ pmd_val(*pmdp) = 0; })
 #define pmd_page(pmd)		virt_to_page(__va(pmd_val(pmd)))
 
 
diff --git a/arch/m68k/include/asm/page.h b/arch/m68k/include/asm/page.h
index 05e1e1e77a9a..c02326b56ae2 100644
--- a/arch/m68k/include/asm/page.h
+++ b/arch/m68k/include/asm/page.h
@@ -22,9 +22,9 @@
  * These are used to make use of C type-checking..
  */
 #if !defined(CONFIG_MMU) || CONFIG_PGTABLE_LEVELS == 3
-typedef struct { unsigned long pmd[16]; } pmd_t;
-#define pmd_val(x)	((&x)->pmd[0])
-#define __pmd(x)	((pmd_t) { { (x) }, })
+typedef struct { unsigned long pmd; } pmd_t;
+#define pmd_val(x)	((&x)->pmd)
+#define __pmd(x)	((pmd_t) { (x) } )
 #endif
 
 typedef struct { unsigned long pte; } pte_t;
diff --git a/arch/m68k/include/asm/pgtable_mm.h b/arch/m68k/include/asm/pgtable_mm.h
index 2bf5c3501e78..f0e5167de834 100644
--- a/arch/m68k/include/asm/pgtable_mm.h
+++ b/arch/m68k/include/asm/pgtable_mm.h
@@ -36,7 +36,7 @@
 
 /* PMD_SHIFT determines the size of the area a second-level page table can map */
 #if CONFIG_PGTABLE_LEVELS == 3
-#define PMD_SHIFT	22
+#define PMD_SHIFT	18
 #endif
 #define PMD_SIZE	(1UL << PMD_SHIFT)
 #define PMD_MASK	(~(PMD_SIZE-1))
@@ -67,8 +67,8 @@
 #define PTRS_PER_PMD	1
 #define PTRS_PER_PGD	1024
 #else
-#define PTRS_PER_PTE	1024
-#define PTRS_PER_PMD	8
+#define PTRS_PER_PTE	64
+#define PTRS_PER_PMD	128
 #define PTRS_PER_PGD	128
 #endif
 #define USER_PTRS_PER_PGD	(TASK_SIZE/PGDIR_SIZE)
@@ -76,8 +76,8 @@
 
 /* Virtual address region for use by kernel_map() */
 #ifdef CONFIG_SUN3
-#define KMAP_START     0x0DC00000
-#define KMAP_END       0x0E000000
+#define KMAP_START	0x0dc00000
+#define KMAP_END	0x0e000000
 #elif defined(CONFIG_COLDFIRE)
 #define KMAP_START	0xe0000000
 #define KMAP_END	0xf0000000