linux-kernel - [PATCH] x86-64: finish clear_highmaps()'s job wrt. _brk

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Message-Id: <4A019977.76EA.0078.0@novell.com>
Date:	Wed, 06 May 2009 13:06:47 +0100
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	<mingo@...e.hu>, <tglx@...utronix.de>, <hpa@...or.com>
Cc:	<linux-kernel@...r.kernel.org>
Subject: [PATCH] x86-64: finish clear_highmaps()'s job wrt. _brk_end

Impact: bug fix

With the introduction of the .brk section, special care must be taken
that no unused page table entries remain if _brk_end and _end are
separated by a 2M page boundary. clear_highmap() runs very early and
hence cannot take care of that, hence potential entries needing to be
removed past _brk_end must be cleared once the brk allocator has done
its job.

Signed-off-by: Jan Beulich <jbeulich@...ell.com>

---
 arch/x86/mm/init.c |   18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

--- linux-2.6.30-rc4/arch/x86/mm/init.c	2009-04-30 09:42:42.000000000 +0200
+++ 2.6.30-rc4-x86_64-brk_end-end/arch/x86/mm/init.c	2009-05-06 13:44:01.000000000 +0200
@@ -7,6 +7,7 @@
 #include <asm/page.h>
 #include <asm/page_types.h>
 #include <asm/sections.h>
+#include <asm/setup.h>
 #include <asm/system.h>
 #include <asm/tlbflush.h>

@@ -304,8 +305,23 @@ unsigned long __init_refok init_memory_m
 #endif

 #ifdef CONFIG_X86_64
-	if (!after_bootmem)
+	if (!after_bootmem && !start) {
+		pud_t *pud;
+		pmd_t *pmd;
+
 		mmu_cr4_features = read_cr4();
+
+		/*
+		 * _brk_end cannot change anymore, but it and _end may be
+		 * located on different 2M pages. cleanup_highmap(), however,
+		 * can only consider _end when it runs, so destroy any
+		 * mappings beyond _brk_end here.
+		 */
+		pud = pud_offset(pgd_offset_k(_brk_end), _brk_end);
+		pmd = pmd_offset(pud, _brk_end - 1);
+		while (++pmd <= pmd_offset(pud, (unsigned long)_end - 1))
+			pmd_clear(pmd);
+	}
 #endif
 	__flush_tlb_all();

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