Encode huge page size for VM_FAULT_HWPOISON errors

This fixes a problem introduced with the hugetlb hwpoison handling

The user space SIGBUS signalling wants to know the size of the hugepage
that caused a HWPOISON fault.

Unfortunately the architecture page fault handlers do not have easy
access to the struct page.

Pass the information out in the fault error code instead.

I added a separate VM_FAULT_HWPOISON_LARGE bit for this case and encode
the hpage index in some free upper bits of the fault code. The small
page hwpoison keeps stays with the VM_FAULT_HWPOISON name to minimize
changes.

Also add code to hugetlb.h to convert that index into a page shift.

Will be used in a further patch.

Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: fengguang.wu@intel.com
Signed-off-by: Andi Kleen <ak@linux.intel.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 67cd03239b75..96991ded82fe 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -2589,7 +2589,8 @@ retry:
                  * So we need to block hugepage fault by PG_hwpoison bit check.
                  */
                 if (unlikely(PageHWPoison(page))) {
-                        ret = VM_FAULT_HWPOISON;
+                        ret = VM_FAULT_HWPOISON | 
+                              VM_FAULT_SET_HINDEX(h - hstates);
                         goto backout_unlocked;
                 }
                 page_dup_rmap(page);
@@ -2656,7 +2657,8 @@ int hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma,
                         migration_entry_wait(mm, (pmd_t *)ptep, address);
                         return 0;
                 } else if (unlikely(is_hugetlb_entry_hwpoisoned(entry)))
-                        return VM_FAULT_HWPOISON;
+                        return VM_FAULT_HWPOISON_LARGE | 
+                               VM_FAULT_SET_HINDEX(h - hstates);
         }
 
         ptep = huge_pte_alloc(mm, address, huge_page_size(h));