[PATCH 3/4] hwpoison: prevent /dev/kcore from accessing hwpoison pages

[Wu Fengguang <fengguang.wu@intel.com>]

[-- Attachment #1: hwpoison-kcore.patch --]
[-- Type: text/plain, Size: 1452 bytes --]

Silently fill buffer with zeros when encounter hwpoison pages
(accessing the hwpoison page content is deadly).

This patch does not cover X86_32 - which has a dumb kern_addr_valid().
It is unlikely anyone run a 32bit kernel will care about the hwpoison
feature - its usable memory is limited.

CC: Ingo Molnar <mingo@elte.hu>
CC: Andi Kleen <andi@firstfloor.org> 
CC: Pekka Enberg <penberg@cs.helsinki.fi>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
 arch/x86/mm/init_64.c |   16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

--- linux-mm.orig/arch/x86/mm/init_64.c	2010-01-13 21:23:04.000000000 +0800
+++ linux-mm/arch/x86/mm/init_64.c	2010-01-13 21:25:32.000000000 +0800
@@ -825,6 +825,7 @@ int __init reserve_bootmem_generic(unsig
 int kern_addr_valid(unsigned long addr)
 {
 	unsigned long above = ((long)addr) >> __VIRTUAL_MASK_SHIFT;
+	unsigned long pfn;
 	pgd_t *pgd;
 	pud_t *pud;
 	pmd_t *pmd;
@@ -845,14 +846,23 @@ int kern_addr_valid(unsigned long addr)
 	if (pmd_none(*pmd))
 		return 0;
 
-	if (pmd_large(*pmd))
-		return pfn_valid(pmd_pfn(*pmd));
+	if (pmd_large(*pmd)) {
+		pfn = pmd_pfn(*pmd);
+		pfn += pte_index(addr);
+		goto check_pfn;
+	}
 
 	pte = pte_offset_kernel(pmd, addr);
 	if (pte_none(*pte))
 		return 0;
 
-	return pfn_valid(pte_pfn(*pte));
+	pfn = pte_pfn(*pte);
+check_pfn:
+	if (!pfn_valid(pfn))
+		return 0;
+	if (PageHWPoison(pfn_to_page(pfn)))
+		return 0;
+	return 1;
 }
 
 /*