x86, mm: setup page table in top-down

Get pgt_buf early from BRK, and use it to map PMD_SIZE from top at first.
Then use mapped pages to map more ranges below, and keep looping until
all pages get mapped.

alloc_low_page will use page from BRK at first, after that buffer is used
up, will use memblock to find and reserve pages for page table usage.

Introduce min_pfn_mapped to make sure find new pages from mapped ranges,
that will be updated when lower pages get mapped.

Also add step_size to make sure that don't try to map too big range with
limited mapped pages initially, and increase the step_size when we have
more mapped pages on hand.

We don't need to call pagetable_reserve anymore, reserve work is done
in alloc_low_page() directly.

At last we can get rid of calculation and find early pgt related code.

-v2: update to after fix_xen change,
     also use MACRO for initial pgt_buf size and add comments with it.
-v3: skip big reserved range in memblock.reserved near end.
-v4: don't need fix_xen change now.
-v5: add changelog about moving about reserving pagetable to alloc_low_page.

Suggested-by: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Link: http://lkml.kernel.org/r/1353123563-3103-22-git-send-email-yinghai@kernel.org
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

arch/x86/include/asm/page_types.h

@@ -45,6 +45,7 @@ extern int devmem_is_allowed(unsigned long pagenr);
 
 extern unsigned long max_low_pfn_mapped;
 extern unsigned long max_pfn_mapped;
+extern unsigned long min_pfn_mapped;
 
 static inline phys_addr_t get_max_mapped(void)
 {

arch/x86/include/asm/pgtable.h

@@ -603,6 +603,7 @@ static inline int pgd_none(pgd_t pgd)
 
 extern int direct_gbpages;
 void init_mem_mapping(void);
+void early_alloc_pgt_buf(void);
 
 /* local pte updates need not use xchg for locking */
 static inline pte_t native_local_ptep_get_and_clear(pte_t *ptep)

arch/x86/kernel/setup.c

@@ -124,6 +124,7 @@
  */
 unsigned long max_low_pfn_mapped;
 unsigned long max_pfn_mapped;
+unsigned long min_pfn_mapped;
 
 #ifdef CONFIG_DMI
 RESERVE_BRK(dmi_alloc, 65536);
@@ -900,6 +901,8 @@ void __init setup_arch(char **cmdline_p)
 
 	reserve_ibft_region();
 
+	early_alloc_pgt_buf();
+
 	/*
 	 * Need to conclude brk, before memblock_x86_fill()
 	 *  it could use memblock_find_in_range, could overlap with

arch/x86/mm/init.c

@@ -21,6 +21,21 @@ unsigned long __initdata pgt_buf_start;
 unsigned long __meminitdata pgt_buf_end;
 unsigned long __meminitdata pgt_buf_top;
 
+/* need 4 4k for initial PMD_SIZE, 4k for 0-ISA_END_ADDRESS */
+#define INIT_PGT_BUF_SIZE	(5 * PAGE_SIZE)
+RESERVE_BRK(early_pgt_alloc, INIT_PGT_BUF_SIZE);
+void  __init early_alloc_pgt_buf(void)
+{
+	unsigned long tables = INIT_PGT_BUF_SIZE;
+	phys_addr_t base;
+
+	base = __pa(extend_brk(tables, PAGE_SIZE));
+
+	pgt_buf_start = base >> PAGE_SHIFT;
+	pgt_buf_end = pgt_buf_start;
+	pgt_buf_top = pgt_buf_start + (tables >> PAGE_SHIFT);
+}
+
 int after_bootmem;
 
 int direct_gbpages
@@ -228,105 +243,6 @@ static int __meminit split_mem_range(struct map_range *mr, int nr_range,
 	return nr_range;
 }
 
-/*
- * First calculate space needed for kernel direct mapping page tables to cover
- * mr[0].start to mr[nr_range - 1].end, while accounting for possible 2M and 1GB
- * pages. Then find enough contiguous space for those page tables.
- */
-static unsigned long __init calculate_table_space_size(unsigned long start, unsigned long end)
-{
-	int i;
-	unsigned long puds = 0, pmds = 0, ptes = 0, tables;
-	struct map_range mr[NR_RANGE_MR];
-	int nr_range;
-
-	memset(mr, 0, sizeof(mr));
-	nr_range = 0;
-	nr_range = split_mem_range(mr, nr_range, start, end);
-
-	for (i = 0; i < nr_range; i++) {
-		unsigned long range, extra;
-
-		range = mr[i].end - mr[i].start;
-		puds += (range + PUD_SIZE - 1) >> PUD_SHIFT;
-
-		if (mr[i].page_size_mask & (1 << PG_LEVEL_1G)) {
-			extra = range - ((range >> PUD_SHIFT) << PUD_SHIFT);
-			pmds += (extra + PMD_SIZE - 1) >> PMD_SHIFT;
-		} else {
-			pmds += (range + PMD_SIZE - 1) >> PMD_SHIFT;
-		}
-
-		if (mr[i].page_size_mask & (1 << PG_LEVEL_2M)) {
-			extra = range - ((range >> PMD_SHIFT) << PMD_SHIFT);
-#ifdef CONFIG_X86_32
-			extra += PMD_SIZE;
-#endif
-			ptes += (extra + PAGE_SIZE - 1) >> PAGE_SHIFT;
-		} else {
-			ptes += (range + PAGE_SIZE - 1) >> PAGE_SHIFT;
-		}
-	}
-
-	tables = roundup(puds * sizeof(pud_t), PAGE_SIZE);
-	tables += roundup(pmds * sizeof(pmd_t), PAGE_SIZE);
-	tables += roundup(ptes * sizeof(pte_t), PAGE_SIZE);
-
-#ifdef CONFIG_X86_32
-	/* for fixmap */
-	tables += roundup(__end_of_fixed_addresses * sizeof(pte_t), PAGE_SIZE);
-#endif
-
-	return tables;
-}
-
-static unsigned long __init calculate_all_table_space_size(void)
-{
-	unsigned long start_pfn, end_pfn;
-	unsigned long tables;
-	int i;
-
-	/* the ISA range is always mapped regardless of memory holes */
-	tables = calculate_table_space_size(0, ISA_END_ADDRESS);
-
-	for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, NULL) {
-		u64 start = start_pfn << PAGE_SHIFT;
-		u64 end = end_pfn << PAGE_SHIFT;
-
-		if (end <= ISA_END_ADDRESS)
-			continue;
-
-		if (start < ISA_END_ADDRESS)
-			start = ISA_END_ADDRESS;
-#ifdef CONFIG_X86_32
-		/* on 32 bit, we only map up to max_low_pfn */
-		if ((start >> PAGE_SHIFT) >= max_low_pfn)
-			continue;
-
-		if ((end >> PAGE_SHIFT) > max_low_pfn)
-			end = max_low_pfn << PAGE_SHIFT;
-#endif
-		tables += calculate_table_space_size(start, end);
-	}
-
-	return tables;
-}
-
-static void __init find_early_table_space(unsigned long start,
-					  unsigned long good_end,
-					  unsigned long tables)
-{
-	phys_addr_t base;
-
-	base = memblock_find_in_range(start, good_end, tables, PAGE_SIZE);
-	if (!base)
-		panic("Cannot find space for the kernel page tables");
-
-	pgt_buf_start = base >> PAGE_SHIFT;
-	pgt_buf_end = pgt_buf_start;
-	pgt_buf_top = pgt_buf_start + (tables >> PAGE_SHIFT);
-}
-
 static struct range pfn_mapped[E820_X_MAX];
 static int nr_pfn_mapped;
 
@@ -391,17 +307,14 @@ unsigned long __init_refok init_memory_mapping(unsigned long start,
 }
 
 /*
- * Iterate through E820 memory map and create direct mappings for only E820_RAM
+ * would have hole in the middle or ends, and only ram parts will be mapped.
- * regions. We cannot simply create direct mappings for all pfns from
- * [0 to max_low_pfn) and [4GB to max_pfn) because of possible memory holes in
- * high addresses that cannot be marked as UC by fixed/variable range MTRRs.
- * Depending on the alignment of E820 ranges, this may possibly result in using
- * smaller size (i.e. 4K instead of 2M or 1G) page tables.
  */
-static void __init init_range_memory_mapping(unsigned long range_start,
+static unsigned long __init init_range_memory_mapping(
+					   unsigned long range_start,
 					   unsigned long range_end)
 {
 	unsigned long start_pfn, end_pfn;
+	unsigned long mapped_ram_size = 0;
 	int i;
 
 	for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, NULL) {
@@ -421,71 +334,70 @@ static void __init init_range_memory_mapping(unsigned long range_start,
 			end = range_end;
 
 		init_memory_mapping(start, end);
+
+		mapped_ram_size += end - start;
 	}
+
+	return mapped_ram_size;
 }
 
+/* (PUD_SHIFT-PMD_SHIFT)/2 */
+#define STEP_SIZE_SHIFT 5
 void __init init_mem_mapping(void)
 {
-	unsigned long tables, good_end, end;
+	unsigned long end, real_end, start, last_start;
+	unsigned long step_size;
+	unsigned long addr;
+	unsigned long mapped_ram_size = 0;
+	unsigned long new_mapped_ram_size;
 
 	probe_page_size_mask();
 
-	/*
-	 * Find space for the kernel direct mapping tables.
-	 *
-	 * Later we should allocate these tables in the local node of the
-	 * memory mapped. Unfortunately this is done currently before the
-	 * nodes are discovered.
-	 */
 #ifdef CONFIG_X86_64
 	end = max_pfn << PAGE_SHIFT;
-	good_end = end;
 #else
 	end = max_low_pfn << PAGE_SHIFT;
-	good_end = max_pfn_mapped << PAGE_SHIFT;
 #endif
-	tables = calculate_all_table_space_size();
-	find_early_table_space(0, good_end, tables);
-	printk(KERN_DEBUG "kernel direct mapping tables up to %#lx @ [mem %#010lx-%#010lx] prealloc\n",
-		end - 1, pgt_buf_start << PAGE_SHIFT,
-		(pgt_buf_top << PAGE_SHIFT) - 1);
 
-	max_pfn_mapped = 0; /* will get exact value next */
 	/* the ISA range is always mapped regardless of memory holes */
 	init_memory_mapping(0, ISA_END_ADDRESS);
-	init_range_memory_mapping(ISA_END_ADDRESS, end);
+
+	/* xen has big range in reserved near end of ram, skip it at first */
+	addr = memblock_find_in_range(ISA_END_ADDRESS, end, PMD_SIZE,
+			 PAGE_SIZE);
+	real_end = addr + PMD_SIZE;
+
+	/* step_size need to be small so pgt_buf from BRK could cover it */
+	step_size = PMD_SIZE;
+	max_pfn_mapped = 0; /* will get exact value next */
+	min_pfn_mapped = real_end >> PAGE_SHIFT;
+	last_start = start = real_end;
+	while (last_start > ISA_END_ADDRESS) {
+		if (last_start > step_size) {
+			start = round_down(last_start - 1, step_size);
+			if (start < ISA_END_ADDRESS)
+				start = ISA_END_ADDRESS;
+		} else
+			start = ISA_END_ADDRESS;
+		new_mapped_ram_size = init_range_memory_mapping(start,
+							last_start);
+		last_start = start;
+		min_pfn_mapped = last_start >> PAGE_SHIFT;
+		/* only increase step_size after big range get mapped */
+		if (new_mapped_ram_size > mapped_ram_size)
+			step_size <<= STEP_SIZE_SHIFT;
+		mapped_ram_size += new_mapped_ram_size;
+	}
+
+	if (real_end < end)
+		init_range_memory_mapping(real_end, end);
+
 #ifdef CONFIG_X86_64
 	if (max_pfn > max_low_pfn) {
 		/* can we preseve max_low_pfn ?*/
 		max_low_pfn = max_pfn;
 	}
 #endif
-	/*
-	 * Reserve the kernel pagetable pages we used (pgt_buf_start -
-	 * pgt_buf_end) and free the other ones (pgt_buf_end - pgt_buf_top)
-	 * so that they can be reused for other purposes.
-	 *
-	 * On native it just means calling memblock_reserve, on Xen it also
-	 * means marking RW the pagetable pages that we allocated before
-	 * but that haven't been used.
-	 *
-	 * In fact on xen we mark RO the whole range pgt_buf_start -
-	 * pgt_buf_top, because we have to make sure that when
-	 * init_memory_mapping reaches the pagetable pages area, it maps
-	 * RO all the pagetable pages, including the ones that are beyond
-	 * pgt_buf_end at that time.
-	 */
-	if (pgt_buf_end > pgt_buf_start) {
-		printk(KERN_DEBUG "kernel direct mapping tables up to %#lx @ [mem %#010lx-%#010lx] final\n",
-			end - 1, pgt_buf_start << PAGE_SHIFT,
-			(pgt_buf_end << PAGE_SHIFT) - 1);
-		x86_init.mapping.pagetable_reserve(PFN_PHYS(pgt_buf_start),
-				PFN_PHYS(pgt_buf_end));
-	}
-
-	/* stop the wrong using */
-	pgt_buf_top = 0;
-
 	early_memtest(0, max_pfn_mapped << PAGE_SHIFT);
 }
 

arch/x86/mm/init_32.c

@@ -61,11 +61,22 @@ bool __read_mostly __vmalloc_start_set = false;
 
 static __init void *alloc_low_page(void)
 {
-	unsigned long pfn = pgt_buf_end++;
+	unsigned long pfn;
 	void *adr;
 
-	if (pfn >= pgt_buf_top)
+	if ((pgt_buf_end + 1) >= pgt_buf_top) {
-		panic("alloc_low_page: ran out of memory");
+		unsigned long ret;
+		if (min_pfn_mapped >= max_pfn_mapped)
+			panic("alloc_low_page: ran out of memory");
+		ret = memblock_find_in_range(min_pfn_mapped << PAGE_SHIFT,
+					max_pfn_mapped << PAGE_SHIFT,
+					PAGE_SIZE, PAGE_SIZE);
+		if (!ret)
+			panic("alloc_low_page: can not alloc memory");
+		memblock_reserve(ret, PAGE_SIZE);
+		pfn = ret >> PAGE_SHIFT;
+	} else
+		pfn = pgt_buf_end++;
 
 	adr = __va(pfn * PAGE_SIZE);
 	clear_page(adr);

arch/x86/mm/init_64.c

@@ -316,7 +316,7 @@ void __init cleanup_highmap(void)
 
 static __ref void *alloc_low_page(unsigned long *phys)
 {
-	unsigned long pfn = pgt_buf_end++;
+	unsigned long pfn;
 	void *adr;
 
 	if (after_bootmem) {
@@ -326,8 +326,19 @@ static __ref void *alloc_low_page(unsigned long *phys)
 		return adr;
 	}
 
-	if (pfn >= pgt_buf_top)
+	if ((pgt_buf_end + 1) >= pgt_buf_top) {
-		panic("alloc_low_page: ran out of memory");
+		unsigned long ret;
+		if (min_pfn_mapped >= max_pfn_mapped)
+			panic("alloc_low_page: ran out of memory");
+		ret = memblock_find_in_range(min_pfn_mapped << PAGE_SHIFT,
+					max_pfn_mapped << PAGE_SHIFT,
+					PAGE_SIZE, PAGE_SIZE);
+		if (!ret)
+			panic("alloc_low_page: can not alloc memory");
+		memblock_reserve(ret, PAGE_SIZE);
+		pfn = ret >> PAGE_SHIFT;
+	} else
+		pfn = pgt_buf_end++;
 
 	adr = early_memremap(pfn * PAGE_SIZE, PAGE_SIZE);
 	clear_page(adr);