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>

1 files changed, 14 insertions, 3 deletions

diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
index 27f7fc69cf8..7bb11064a9e 100644
--- a/arch/x86/mm/init_32.c
+++ b/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)
-		panic("alloc_low_page: ran out of memory");
+	if ((pgt_buf_end + 1) >= pgt_buf_top) {
+		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);