[PATCH] 18pre7aa1 mm init

[Hugh Dickins]

Thanks for putting in my HIGHMEM64G 3GB,2GB,1GB menu; but I was
sorry you didn't integrate the corresponding arch/i386/mm/init.c,
choosing instead to make fixrange_init yet more complicated...

There are at least three bugs there, I gave up and went back to
the version I tested before instead of trying to patch up yours.

The three bugs I found (1GB uvirtual 2GB physical HIGHMEM64G):
1. You use a pgd_none test in your CONFIG_X86_PAE additions to
   fixrange_init, but pgd_none always 0 when PAE: you'd have to
   compare against empty_zero_page instead.
2. You calculate nr_pte one too few since start is not PMD_SIZE
   aligned, so final page table still discontiguous in some cases
   e.g. when it finds it does need to allocate another pmd.
3. If 1GB uvirtual 1GB physical HIGHMEM64G then pgd[2]
   will remain empty_zero_page, and vmallocs will fail.
   
Imagine my distress if next time around I discover you've
fixed those three with even more code in fixrange_init!
Patch rediffed below.

Hugh

--- 2.4.18-pre7aa1/arch/i386/mm/init.c	Wed Jan 30 15:10:34 2002
+++ linux/arch/i386/mm/init.c	Wed Jan 30 20:02:17 2002
@@ -167,69 +167,6 @@
 	set_pte_phys(address, phys, flags);
 }
 
-static void __init fixrange_init (unsigned long start, unsigned long end, pgd_t *pgd_base, int contigous_pte)
-{
-	pgd_t *pgd;
-	pmd_t *pmd;
-	pte_t *pte;
-	int i, j;
-	int nr_pte;
-	void * pte_array;
-
-	if (start & ~PAGE_MASK)
-		BUG();
-
-	i = __pgd_offset(start);
-	j = __pmd_offset(start);
-	pgd = pgd_base + i;
-
-	if (contigous_pte) {
-		if (start >= end)
-			BUG();
-		nr_pte = (end - start + PMD_SIZE - 1) >> PMD_SHIFT;
-#if CONFIG_X86_PAE
-		/* no pmd w/o PAE enabled */
-		if (j + nr_pte > PTRS_PER_PMD)
-			BUG();
-#endif
-		pte_array = alloc_bootmem_low_pages(PAGE_SIZE * nr_pte);
-	}
-	for ( ; (i < PTRS_PER_PGD) && (start < end); pgd++, i++) {
-#if CONFIG_X86_PAE
-		if (pgd_none(*pgd)) {
-			pmd = (pmd_t *) alloc_bootmem_low_pages(PAGE_SIZE);
-			set_pgd(pgd, __pgd(__pa(pmd) + 0x1));
-			if (pmd != pmd_offset(pgd, 0))
-				printk("PAE BUG #02!\n");
-		}
-		pmd = pmd_offset(pgd, start);
-#else
-		pmd = (pmd_t *)pgd;
-#endif
-		for (; (j < PTRS_PER_PMD) && (start < end); pmd++, j++) {
-			if (pmd_none(*pmd)) {
-				if (contigous_pte) {
-					pte = (pte_t *) pte_array;
-					pte_array += PAGE_SIZE;
-					nr_pte--;
-				} else
-					pte = (pte_t *) alloc_bootmem_low_pages(PAGE_SIZE);
-				set_pmd(pmd, mk_pmd_phys(__pa(pte), __pgprot(_KERNPG_TABLE)));
-				if (pte != pte_offset_lowmem(pmd, 0))
-					BUG();
-			}
-			start += PMD_SIZE;
-		}
-		j = 0;
-	}
-	if (contigous_pte) {
-		if (nr_pte < 0)
-			BUG();
-		if (nr_pte > 0)
-			free_bootmem((unsigned long) pte_array, nr_pte * PAGE_SIZE);
-	}
-}
-
 static void __init pagetable_init (void)
 {
 	unsigned long vaddr, end;
@@ -246,8 +183,24 @@
 
 	pgd_base = swapper_pg_dir;
 #if CONFIG_X86_PAE
-	for (i = 0; i < PTRS_PER_PGD; i++)
+	/*
+	 * First set all four entries of the pgd.
+	 * Usually only one page is needed here: if PAGE_OFFSET lowered,
+	 * maybe three pages: need not be contiguous, but might as well.
+	 */
+	pmd = (pmd_t *)alloc_bootmem_low_pages(KERNEL_PGD_PTRS*PAGE_SIZE);
+	for (i = 1; i < USER_PGD_PTRS; i++)
 		set_pgd(pgd_base + i, __pgd(1 + __pa(empty_zero_page)));
+	for (; i < PTRS_PER_PGD; i++, pmd += PTRS_PER_PMD)
+		set_pgd(pgd_base + i, __pgd(1 + __pa(pmd)));
+	/*
+	 * Add low memory identity-mappings - SMP needs it when
+	 * starting up on an AP from real-mode. In the non-PAE
+	 * case we already have these mappings through head.S.
+	 * All user-space mappings are explicitly cleared after
+	 * SMP startup.
+	 */
+	pgd_base[0] = pgd_base[USER_PGD_PTRS];
 #endif
 	i = __pgd_offset(PAGE_OFFSET);
 	pgd = pgd_base + i;
@@ -256,14 +209,7 @@
 		vaddr = i*PGDIR_SIZE;
 		if (end && (vaddr >= end))
 			break;
-#if CONFIG_X86_PAE
-		pmd = (pmd_t *) alloc_bootmem_low_pages(PAGE_SIZE);
-		set_pgd(pgd, __pgd(__pa(pmd) + 0x1));
-#else
-		pmd = (pmd_t *)pgd;
-#endif
-		if (pmd != pmd_offset(pgd, 0))
-			BUG();
+		pmd = pmd_offset(pgd, 0);
 		for (j = 0; j < PTRS_PER_PMD; pmd++, j++) {
 			vaddr = i*PGDIR_SIZE + j*PMD_SIZE;
 			if (end && (vaddr >= end))
@@ -298,36 +244,28 @@
 		}
 	}
 
-#if CONFIG_HIGHMEM
 	/*
-	 * Permanent kmaps: initialize before the fixmap area
-	 * because here the ptes needs to be contigous.
+	 * Leave vmalloc() to create its own page tables as needed,
+	 * but create the page tables at top of virtual memory, to be
+	 * populated by kmap_high(), kmap_atomic(), and set_fixmap().
+	 * kmap_high() assumes pkmap_page_table contiguous throughout.
 	 */
+#if CONFIG_HIGHMEM
 	vaddr = PKMAP_BASE;
-	fixrange_init(vaddr, vaddr + PKMAP_SIZE, pgd_base, 1);
+#else
+	vaddr = FIXADDR_START;
+#endif
+	pmd = pmd_offset(pgd_offset_k(vaddr), vaddr);
+	i = (0UL - (vaddr & PMD_MASK)) >> PMD_SHIFT;
+	pte = (pte_t *)alloc_bootmem_low_pages(i*PAGE_SIZE);
+	for (; --i >= 0; pmd++, pte += PTRS_PER_PTE)
+		set_pmd(pmd, mk_pmd_phys(__pa(pte), __pgprot(_KERNPG_TABLE)));
 
+#if CONFIG_HIGHMEM
 	pgd = swapper_pg_dir + __pgd_offset(vaddr);
 	pmd = pmd_offset(pgd, vaddr);
 	pte = pte_offset_lowmem(pmd, vaddr);
 	pkmap_page_table = pte;
-#endif
-
-	/*
-	 * Fixed mappings, only the page table structure has to be
-	 * created - mappings will be set by set_fixmap():
-	 */
-	vaddr = FIXADDR_START;
-	fixrange_init(vaddr, vaddr + FIXADDR_SIZE, pgd_base, 0);
-
-#if CONFIG_X86_PAE
-	/*
-	 * Add low memory identity-mappings - SMP needs it when
-	 * starting up on an AP from real-mode. In the non-PAE
-	 * case we already have these mappings through head.S.
-	 * All user-space mappings are explicitly cleared after
-	 * SMP startup.
-	 */
-	pgd_base[0] = pgd_base[USER_PTRS_PER_PGD];
 #endif
 }