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

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Date:	Tue, 01 Jul 2008 16:46:32 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
	Stephen Tweedie <sct@...hat.com>,
	Eduardo Habkost <ehabkost@...hat.com>,
	Mark McLoughlin <markmc@...hat.com>, x86@...nel.org
Subject: [PATCH 3 of 8] x86_64/setup: preserve existing PUD mappings

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@...rix.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)


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