userfaultfd: hugetlbfs: add userfaultfd hugetlb hook

When processing a hugetlb fault for no page present, check the vma to
determine if faults are to be handled via userfaultfd.  If so, drop the
hugetlb_fault_mutex and call handle_userfault().

Link: http://lkml.kernel.org/r/20161216144821.5183-21-aarcange@redhat.com
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Michael Rapoport <RAPOPORT@il.ibm.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 5d20af9..a4b2905 100644 (file)
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -32,6 +32,7 @@
 #include <linux/hugetlb.h>
 #include <linux/hugetlb_cgroup.h>
 #include <linux/node.h>
+#include <linux/userfaultfd_k.h>
 #include "internal.h"
 
 int hugepages_treat_as_movable;
@@ -3680,6 +3681,38 @@ retry:
                size = i_size_read(mapping->host) >> huge_page_shift(h);
                if (idx >= size)
                        goto out;
+
+               /*
+                * Check for page in userfault range
+                */
+               if (userfaultfd_missing(vma)) {
+                       u32 hash;
+                       struct vm_fault vmf = {
+                               .vma = vma,
+                               .address = address,
+                               .flags = flags,
+                               /*
+                                * Hard to debug if it ends up being
+                                * used by a callee that assumes
+                                * something about the other
+                                * uninitialized fields... same as in
+                                * memory.c
+                                */
+                       };
+
+                       /*
+                        * hugetlb_fault_mutex must be dropped before
+                        * handling userfault.  Reacquire after handling
+                        * fault to make calling code simpler.
+                        */
+                       hash = hugetlb_fault_mutex_hash(h, mm, vma, mapping,
+                                                       idx, address);
+                       mutex_unlock(&hugetlb_fault_mutex_table[hash]);
+                       ret = handle_userfault(&vmf, VM_UFFD_MISSING);
+                       mutex_lock(&hugetlb_fault_mutex_table[hash]);
+                       goto out;
+               }
+
                page = alloc_huge_page(vma, address, 0);
                if (IS_ERR(page)) {
                        ret = PTR_ERR(page);