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Subject[PATCH 7/8] HWPOISON, hugetlb: detect hwpoison in hugetlb code
Date
This patch enables to block access to hwpoisoned hugepage and
also enables to block unmapping for it.

Dependency:
"HWPOISON, hugetlb: enable error handling path for hugepage"

Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Wu Fengguang <fengguang.wu@intel.com>
---
mm/hugetlb.c | 40 ++++++++++++++++++++++++++++++++++++++++
1 files changed, 40 insertions(+), 0 deletions(-)
diff --git v2.6.34/mm/hugetlb.c v2.6.34/mm/hugetlb.c
index aaba3cc..5580568 100644
--- v2.6.34/mm/hugetlb.c
+++ v2.6.34/mm/hugetlb.c
@@ -19,6 +19,8 @@
#include <linux/sysfs.h>
#include <linux/slab.h>
#include <linux/rmap.h>
+#include <linux/swap.h>
+#include <linux/swapops.h>

#include <asm/page.h>
#include <asm/pgtable.h>
@@ -2145,6 +2147,19 @@ nomem:
return -ENOMEM;
}

+static int is_hugetlb_entry_hwpoisoned(pte_t pte)
+{
+ swp_entry_t swp;
+
+ if (huge_pte_none(pte) || pte_present(pte))
+ return 0;
+ swp = pte_to_swp_entry(pte);
+ if (non_swap_entry(swp) && is_hwpoison_entry(swp)) {
+ return 1;
+ } else
+ return 0;
+}
+
void __unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start,
unsigned long end, struct page *ref_page)
{
@@ -2203,6 +2218,12 @@ void __unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start,
if (huge_pte_none(pte))
continue;

+ /*
+ * HWPoisoned hugepage is already unmapped and dropped reference
+ */
+ if (unlikely(is_hugetlb_entry_hwpoisoned(pte)))
+ continue;
+
page = pte_page(pte);
if (pte_dirty(pte))
set_page_dirty(page);
@@ -2487,6 +2508,18 @@ retry:
}

/*
+ * Since memory error handler replaces pte into hwpoison swap entry
+ * at the time of error handling, a process which reserved but not have
+ * the mapping to the error hugepage does not have hwpoison swap entry.
+ * So we need to block accesses from such a process by checking
+ * PG_hwpoison bit here.
+ */
+ if (unlikely(PageHWPoison(page))) {
+ ret = VM_FAULT_HWPOISON;
+ goto backout_unlocked;
+ }
+
+ /*
* If we are going to COW a private mapping later, we examine the
* pending reservations for this page now. This will ensure that
* any allocations necessary to record that reservation occur outside
@@ -2540,6 +2573,13 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
static DEFINE_MUTEX(hugetlb_instantiation_mutex);
struct hstate *h = hstate_vma(vma);

+ ptep = huge_pte_offset(mm, address);
+ if (ptep) {
+ entry = huge_ptep_get(ptep);
+ if (unlikely(is_hugetlb_entry_hwpoisoned(entry)))
+ return VM_FAULT_HWPOISON;
+ }
+
ptep = huge_pte_alloc(mm, address, huge_page_size(h));
if (!ptep)
return VM_FAULT_OOM;
--
1.7.0


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