On Fri, Aug 31, 2018 at 12:05:38AM +1000, Balbir Singh wrote:
On Fri, Aug 24, 2018 at 03:25:44PM -0400, jglisse@redhat.com wrote:
From: Ralph Campbell rcampbell@nvidia.com
Private ZONE_DEVICE pages use a special pte entry and thus are not present. Properly handle this case in map_pte(), it is already handled in check_pte(), the map_pte() part was lost in some rebase most probably.
Without this patch the slow migration path can not migrate back private ZONE_DEVICE memory to regular memory. This was found after stress testing migration back to system memory. This ultimatly can lead the CPU to an infinite page fault loop on the special swap entry.
Signed-off-by: Ralph Campbell rcampbell@nvidia.com Signed-off-by: Jérôme Glisse jglisse@redhat.com Cc: Andrew Morton akpm@linux-foundation.org Cc: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc: stable@vger.kernel.org
mm/page_vma_mapped.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c index ae3c2a35d61b..1cf5b9bfb559 100644 --- a/mm/page_vma_mapped.c +++ b/mm/page_vma_mapped.c @@ -21,6 +21,15 @@ static bool map_pte(struct page_vma_mapped_walk *pvmw) if (!is_swap_pte(*pvmw->pte)) return false; } else {
if (is_swap_pte(*pvmw->pte)) {swp_entry_t entry;/* Handle un-addressable ZONE_DEVICE memory */entry = pte_to_swp_entry(*pvmw->pte);if (is_device_private_entry(entry))return true;}This happens just for !PVMW_SYNC && PVMW_MIGRATION? I presume this is triggered via the remove_migration_pte() code path? Doesn't returning true here imply that we've taken the ptl lock for the pvmw?
This happens through try_to_unmap() from migrate_vma_unmap() and thus has !PVMW_SYNC and !PVMW_MIGRATION
But you are right about the ptl lock, so looking at code we were just doing pte modification without holding the pte lock but the page_vma_mapped_walk() would not try to unlock as pvmw->ptl == NULL so this never triggered any warning.
I am gonna post a v2 shortly which address that.
Cheers, Jérôme