3 files changed, 48 insertions, 3 deletions

diff --git a/arch/arm/include/asm/pgtable-2level.h b/arch/arm/include/asm/pgtable-2level.h
index f97ee02..86a659a 100644
--- a/arch/arm/include/asm/pgtable-2level.h
+++ b/arch/arm/include/asm/pgtable-2level.h
@@ -181,6 +181,13 @@ static inline pmd_t *pmd_offset(pud_t *pud, unsigned long addr)
 
 #define set_pte_ext(ptep,pte,ext) cpu_set_pte_ext(ptep,pte,ext)
 
+/*
+ * We don't have huge page support for short descriptors, for the moment
+ * define empty stubs for use by pin_page_for_write.
+ */
+#define pmd_hugewillfault(pmd)	(0)
+#define pmd_thp_or_huge(pmd)	(0)
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* _ASM_PGTABLE_2LEVEL_H */
diff --git a/arch/arm/include/asm/pgtable-3level.h b/arch/arm/include/asm/pgtable-3level.h
index 5689c18..39c54cf 100644
--- a/arch/arm/include/asm/pgtable-3level.h
+++ b/arch/arm/include/asm/pgtable-3level.h
@@ -206,6 +206,9 @@ static inline pmd_t *pmd_offset(pud_t *pud, unsigned long addr)
 #define __HAVE_ARCH_PMD_WRITE
 #define pmd_write(pmd)		(!(pmd_val(pmd) & PMD_SECT_RDONLY))
 
+#define pmd_hugewillfault(pmd)	(!pmd_young(pmd) || !pmd_write(pmd))
+#define pmd_thp_or_huge(pmd)	(pmd_huge(pmd) || pmd_trans_huge(pmd))
+
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 #define pmd_trans_huge(pmd)	(pmd_val(pmd) && !(pmd_val(pmd) & PMD_TABLE_BIT))
 #define pmd_trans_splitting(pmd) (pmd_val(pmd) & PMD_SECT_SPLITTING)
diff --git a/arch/arm/lib/uaccess_with_memcpy.c b/arch/arm/lib/uaccess_with_memcpy.c
index 025f742..3e58d71 100644
--- a/arch/arm/lib/uaccess_with_memcpy.c
+++ b/arch/arm/lib/uaccess_with_memcpy.c
@@ -18,6 +18,7 @@
 #include <linux/hardirq.h> /* for in_atomic() */
 #include <linux/gfp.h>
 #include <linux/highmem.h>
+#include <linux/hugetlb.h>
 #include <asm/current.h>
 #include <asm/page.h>
 
@@ -40,7 +41,35 @@ pin_page_for_write(const void __user *_addr, pte_t **ptep, spinlock_t **ptlp)
 		return 0;
 
 	pmd = pmd_offset(pud, addr);
-	if (unlikely(pmd_none(*pmd) || pmd_bad(*pmd)))
+	if (unlikely(pmd_none(*pmd)))
+		return 0;
+
+	/*
+	 * A pmd can be bad if it refers to a HugeTLB or THP page.
+	 *
+	 * Both THP and HugeTLB pages have the same pmd layout
+	 * and should not be manipulated by the pte functions.
+	 *
+	 * Lock the page table for the destination and check
+	 * to see that it's still huge and whether or not we will
+	 * need to fault on write, or if we have a splitting THP.
+	 */
+	if (unlikely(pmd_thp_or_huge(*pmd))) {
+		ptl = &current->mm->page_table_lock;
+		spin_lock(ptl);
+		if (unlikely(!pmd_thp_or_huge(*pmd)
+			|| pmd_hugewillfault(*pmd)
+			|| pmd_trans_splitting(*pmd))) {
+			spin_unlock(ptl);
+			return 0;
+		}
+
+		*ptep = NULL;
+		*ptlp = ptl;
+		return 1;
+	}
+
+	if (unlikely(pmd_bad(*pmd)))
 		return 0;
 
 	pte = pte_offset_map_lock(current->mm, pmd, addr, &ptl);
@@ -94,7 +123,10 @@ __copy_to_user_memcpy(void __user *to, const void *from, unsigned long n)
 		from += tocopy;
 		n -= tocopy;
 
-		pte_unmap_unlock(pte, ptl);
+		if (pte)
+			pte_unmap_unlock(pte, ptl);
+		else
+			spin_unlock(ptl);
 	}
 	if (!atomic)
 		up_read(&current->mm->mmap_sem);
@@ -147,7 +179,10 @@ __clear_user_memset(void __user *addr, unsigned long n)
 		addr += tocopy;
 		n -= tocopy;
 
-		pte_unmap_unlock(pte, ptl);
+		if (pte)
+			pte_unmap_unlock(pte, ptl);
+		else
+			spin_unlock(ptl);
 	}
 	up_read(&current->mm->mmap_sem);