[PATCH] hugetlb: check for brk() entering a hugepage region

Unlike mmap(), the codepath for brk() creates a vma without first checking
that it doesn't touch a region exclusively reserved for hugepages. On
powerpc, this can allow it to create a normal page vma in a hugepage
region, causing oopses and other badness.

Add a test to prevent this. With this patch, brk() will simply fail if it
attempts to move the break into a hugepage reserved region.

Signed-off-by: David Gibson <[e-mail]>
Cc: Adam Litke <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

mm/mmap.c

···
 	if ((addr + len) > TASK_SIZE || (addr + len) < addr)
 		return -EINVAL;
 
+	error = is_hugepage_only_range(current->mm, addr, len);
+	if (error)
+		return error;
+
 	flags = VM_DATA_DEFAULT_FLAGS | VM_ACCOUNT | mm->def_flags;
 
 	error = arch_mmap_check(addr, len, flags);