userfaultfd: hugetlbfs: fix new flag usage in error path

In commit d6995da31122 ("hugetlb: use page.private for hugetlb specific
page flags") the use of PagePrivate to indicate a reservation count
should be restored at free time was changed to the hugetlb specific flag
HPageRestoreReserve.  Changes to a userfaultfd error path as well as a
VM_BUG_ON() in remove_inode_hugepages() were overlooked.

Users could see incorrect hugetlb reserve counts if they experience an
error with a UFFDIO_COPY operation.  Specifically, this would be the
result of an unlikely copy_huge_page_from_user error.  There is not an
increased chance of hitting the VM_BUG_ON.

Link: https://lkml.kernel.org/r/20210521233952.236434-1-mike.kravetz@oracle.com
Fixes: d6995da31122 ("hugetlb: use page.private for hugetlb specific page flags")
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Mina Almasry <almasry.mina@google.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 9d9e0097c1d3864ff62399a7111e63af92725acb..55efd3dd04f621643f928b9292f81b8ac6331284 100644 (file)
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -529,7 +529,7 @@ static void remove_inode_hugepages(struct inode *inode, loff_t lstart,
                         * the subpool and global reserve usage count can need
                         * to be adjusted.
                         */
-                       VM_BUG_ON(PagePrivate(page));
+                       VM_BUG_ON(HPageRestoreReserve(page));
                        remove_huge_page(page);
                        freed++;
                        if (!truncate_op) {

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index e14b3820c6a814ec3962227cc7dbdc52ffc72a50..63a73e164d5510fba964eec777b7486b634a1343 100644 (file)
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -360,38 +360,38 @@ out:
                 * If a reservation for the page existed in the reservation
                 * map of a private mapping, the map was modified to indicate
                 * the reservation was consumed when the page was allocated.
-                * We clear the PagePrivate flag now so that the global
+                * We clear the HPageRestoreReserve flag now so that the global
                 * reserve count will not be incremented in free_huge_page.
                 * The reservation map will still indicate the reservation
                 * was consumed and possibly prevent later page allocation.
                 * This is better than leaking a global reservation.  If no
-                * reservation existed, it is still safe to clear PagePrivate
-                * as no adjustments to reservation counts were made during
-                * allocation.
+                * reservation existed, it is still safe to clear
+                * HPageRestoreReserve as no adjustments to reservation counts
+                * were made during allocation.
                 *
                 * The reservation map for shared mappings indicates which
                 * pages have reservations.  When a huge page is allocated
                 * for an address with a reservation, no change is made to
-                * the reserve map.  In this case PagePrivate will be set
-                * to indicate that the global reservation count should be
+                * the reserve map.  In this case HPageRestoreReserve will be
+                * set to indicate that the global reservation count should be
                 * incremented when the page is freed.  This is the desired
                 * behavior.  However, when a huge page is allocated for an
                 * address without a reservation a reservation entry is added
-                * to the reservation map, and PagePrivate will not be set.
-                * When the page is freed, the global reserve count will NOT
-                * be incremented and it will appear as though we have leaked
-                * reserved page.  In this case, set PagePrivate so that the
-                * global reserve count will be incremented to match the
-                * reservation map entry which was created.
+                * to the reservation map, and HPageRestoreReserve will not be
+                * set. When the page is freed, the global reserve count will
+                * NOT be incremented and it will appear as though we have
+                * leaked reserved page.  In this case, set HPageRestoreReserve
+                * so that the global reserve count will be incremented to
+                * match the reservation map entry which was created.
                 *
                 * Note that vm_alloc_shared is based on the flags of the vma
                 * for which the page was originally allocated.  dst_vma could
                 * be different or NULL on error.
                 */
                if (vm_alloc_shared)
-                       SetPagePrivate(page);
+                       SetHPageRestoreReserve(page);
                else
-                       ClearPagePrivate(page);
+                       ClearHPageRestoreReserve(page);
                put_page(page);
        }
        BUG_ON(copied < 0);