[PATCH] mm: properly handle fault on huge page migration

[Jerome Glisse]

When huge page is being migrated it's pmd is non zero but does not have
any of the huge pmd flags set. It's a swap entry pmd. The handle_mm_fault
never check for this case and thus if a fault happen in the huge page
range while it's being migrated handle_mm_fault will interpret badly the
pmd.

Signed-off-by: Jerome Glisse <jglisse@xxxxxxxxxx>
---
 mm/memory.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/mm/memory.c b/mm/memory.c
index 6dc1882..e2a039c 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3793,6 +3793,7 @@ retry:
 							  pmd, flags);
 	} else {
 		pmd_t orig_pmd = *pmd;
+		swp_entry_t entry;
 		int ret;
 
 		barrier();
@@ -3829,6 +3830,20 @@ retry:
 
 			return 0;
 		}
+
+		swp_entry_t entry = pte_to_swp_entry((pte_t)orig_pmd);
+		if (unlikely(non_swap_entry(entry))) {
+			if (is_migration_entry(entry)) {
+				migration_entry_wait(mm, pmd, address);
+				/* Retry the fault */
+				return 0;
+			} else if (is_hwpoison_entry(entry)) {
+				return VM_FAULT_HWPOISON;
+			} else {
+				/* Something else is wrong invalid pmd print it ? */
+				return VM_FAULT_SIGBUS;
+			}
+		}
 	}
 
 	if (pmd_numa(*pmd))
-- 
1.7.11.7


--KsGdsel6WgEHnImy--
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