HWPOISON, hugetlb: detect hwpoison in hugetlb code

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: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Fengguang Wu <fengguang.wu@intel.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

1 files changed, 40 insertions, 0 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 8c163f64cf10..4c2efc0f3919 100644
--- a/mm/hugetlb.c
+++ b/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>
@@ -2149,6 +2151,19 @@ 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)
 {
@@ -2207,6 +2222,12 @@ 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);
@@ -2491,6 +2512,18 @@ 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
@@ -2544,6 +2577,13 @@ 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;