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userfaultfd: hugetlbfs: fix new flag usage in error path

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In commit d6995da311 ("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: d6995da311 ("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>
This commit is contained in:
Mike Kravetz 2021-05-22 17:42:11 -07:00 committed by Linus Torvalds
parent 1b6d63938a
commit e32905e573
2 changed files with 15 additions and 15 deletions
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2
fs/hugetlbfs/inode.c
View File

@ -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) {

28
mm/userfaultfd.c
View File

@ -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);