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>

4 files changed, 22 insertions, 5 deletions

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 796f30e00806..943c76b3d4bb 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -307,6 +307,11 @@ static inline struct hstate *page_hstate(struct page *page)
         return size_to_hstate(PAGE_SIZE << compound_order(page));
 }
 
+static inline unsigned hstate_index_to_shift(unsigned index)
+{
+        return hstates[index].order + PAGE_SHIFT;
+}
+
 #else
 struct hstate {};
 #define alloc_huge_page_node(h, nid) NULL
@@ -324,6 +329,7 @@ static inline unsigned int pages_per_huge_page(struct hstate *h)
 {
         return 1;
 }
+#define hstate_index_to_shift(index) 0
 #endif
 
 #endif /* _LINUX_HUGETLB_H */
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 74949fbef8c6..f7e9efc6720b 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -718,12 +718,20 @@ static inline int page_mapped(struct page *page)
 #define VM_FAULT_SIGBUS 0x0002
 #define VM_FAULT_MAJOR  0x0004
 #define VM_FAULT_WRITE  0x0008  /* Special case for get_user_pages */
-#define VM_FAULT_HWPOISON 0x0010        /* Hit poisoned page */
+#define VM_FAULT_HWPOISON 0x0010        /* Hit poisoned small page */
+#define VM_FAULT_HWPOISON_LARGE 0x0020  /* Hit poisoned large page. Index encoded in upper bits */
 
 #define VM_FAULT_NOPAGE 0x0100  /* ->fault installed the pte, not return page */
 #define VM_FAULT_LOCKED 0x0200  /* ->fault locked the returned page */
 
-#define VM_FAULT_ERROR  (VM_FAULT_OOM | VM_FAULT_SIGBUS | VM_FAULT_HWPOISON)
+#define VM_FAULT_HWPOISON_LARGE_MASK 0xf000 /* encodes hpage index for large hwpoison */
+
+#define VM_FAULT_ERROR  (VM_FAULT_OOM | VM_FAULT_SIGBUS | VM_FAULT_HWPOISON | \
+                         VM_FAULT_HWPOISON_LARGE)
+
+/* Encode hstate index for a hwpoisoned large page */
+#define VM_FAULT_SET_HINDEX(x) ((x) << 12)
+#define VM_FAULT_GET_HINDEX(x) (((x) >> 12) & 0xf)
 
 /*
  * Can be called by the pagefault handler when it gets a VM_FAULT_OOM.
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));
diff --git a/mm/memory.c b/mm/memory.c
index 0e18b4d649ec..c2d6dd315659 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1450,7 +1450,8 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
                                         if (ret & VM_FAULT_OOM)
                                                 return i ? i : -ENOMEM;
                                         if (ret &
-                                            (VM_FAULT_HWPOISON|VM_FAULT_SIGBUS))
+                                            (VM_FAULT_HWPOISON|VM_FAULT_HWPOISON_LARGE|
+                                             VM_FAULT_SIGBUS))
                                                 return i ? i : -EFAULT;
                                         BUG();
                                 }