mm/hmm: fix clarify fault logic for device private memoryhmm-4.17

For device private memory caller of hmm_vma_fault() want to be able to
carefully control fault. So update logic to only fault device private
entry if explicitly ask. Before this patch a read only device private
CPU page table entry would fault if caller asked for write without the
device private flag set (in caller flag fault request). After this
patch it will only fault if the device private flag is also set.

Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
Cc: Evgeny Baskakov <ebaskakov@nvidia.com>
Cc: Mark Hairgrove <mhairgrove@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>

1 files changed, 12 insertions, 8 deletions

diff --git a/mm/hmm.c b/mm/hmm.c
index ba912da1c1a1..34aa0b96ba6e 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -390,18 +390,22 @@ static inline void hmm_pte_need_fault(const struct hmm_vma_walk *hmm_vma_walk,
 	/* We aren't ask to do anything ... */
 	if (!(pfns & range->flags[HMM_PFN_VALID]))
 		return;
+	/* If this is device memory than only fault if explicitly ask */
+	if ((cpu_flags & range->flags[HMM_PFN_DEVICE_PRIVATE])) {
+		/* Do we fault on device memory ? */
+		if (pfns & range->flags[HMM_PFN_DEVICE_PRIVATE]) {
+			*write_fault = pfns & range->flags[HMM_PFN_WRITE];
+			*fault = true;
+		}
+		return;
+	}
+
 	/* If CPU page table is not valid then we need to fault */
-	*fault = cpu_flags & range->flags[HMM_PFN_VALID];
+	*fault = !(cpu_flags & range->flags[HMM_PFN_VALID]);
 	/* Need to write fault ? */
 	if ((pfns & range->flags[HMM_PFN_WRITE]) &&
 	    !(cpu_flags & range->flags[HMM_PFN_WRITE])) {
-		*fault = *write_fault = false;
-		return;
-	}
-	/* Do we fault on device memory ? */
-	if ((pfns & range->flags[HMM_PFN_DEVICE_PRIVATE]) &&
-	    (cpu_flags & range->flags[HMM_PFN_DEVICE_PRIVATE])) {
-		*write_fault = pfns & range->flags[HMM_PFN_WRITE];
+		*write_fault = true;
 		*fault = true;
 	}
 }