[PATCH 3 of 8] x86_64/setup: preserve existing PUD mappings

[Jeremy Fitzhardinge <jeremy@goop.org>]

When constructing the physical mapping, reuse any existing PUD pages
rather than starting afresh.  This preserves any special mappings the
earlier boot code may have created.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
---
 arch/x86/mm/init_64.c |   20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -493,6 +493,14 @@
 }
 #endif
 
+static unsigned long __meminit
+phys_pud_update(pgd_t *pgd, unsigned long addr, unsigned long end)
+{
+	pud_t *pud = (pud_t *)pgd_page_vaddr(*pgd);
+
+	return phys_pud_init(pud, addr, end);
+}
+
 /*
  * Setup the direct mapping of the physical memory at PAGE_OFFSET.
  * This runs before bootmem is initialized and gets pages directly from
@@ -525,14 +533,20 @@
 		unsigned long pud_phys;
 		pud_t *pud;
 
+		next = start + PGDIR_SIZE;
+		if (next > end)
+			next = end;
+
+		if (pgd_val(*pgd)) {
+			last_map_addr = phys_pud_update(pgd, __pa(start), __pa(end));
+			continue;
+		}
+
 		if (after_bootmem)
 			pud = pud_offset(pgd, start & PGDIR_MASK);
 		else
 			pud = alloc_low_page(&pud_phys);
 
-		next = start + PGDIR_SIZE;
-		if (next > end)
-			next = end;
 		last_map_addr = phys_pud_init(pud, __pa(start), __pa(next));
 		unmap_low_page(pud);
 		if (!after_bootmem)