[PATCH V3 6/9] dax/fsdev: fail probe on invalid pgmap offset

[John Groves]

From: John Groves <John@xxxxxxxxxx>

Convert the WARN_ON to a fatal error when pgmap_phys > phys. This
condition means the remapped region starts after the device's data
region, which is an impossible state. Previously the probe continued
with data_offset=0, leaving virt_addr silently misaligned. Now probe
returns -EINVAL with a diagnostic message.

Fixes: 759455848df0b ("dax: Save the kva from memremap")
Signed-off-by: John Groves <john@xxxxxxxxxx>
---
 drivers/dax/fsdev.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/dax/fsdev.c b/drivers/dax/fsdev.c
index a2d2eb20fb4d0..aac0130ab2833 100644
--- a/drivers/dax/fsdev.c
+++ b/drivers/dax/fsdev.c
@@ -310,8 +310,13 @@ static int fsdev_dax_probe(struct dev_dax *dev_dax)
 		u64 phys = dev_dax->ranges[0].range.start;
 		u64 pgmap_phys = dev_dax->pgmap[0].range.start;
 
-		if (!WARN_ON(pgmap_phys > phys))
-			data_offset = phys - pgmap_phys;
+		if (pgmap_phys > phys) {
+			dev_err(dev, "pgmap start %#llx exceeds data start %#llx\n",
+				pgmap_phys, phys);
+			rc = -EINVAL;
+			goto err_pgmap;
+		}
+		data_offset = phys - pgmap_phys;
 
 		pr_debug("%s: offset detected phys=%llx pgmap_phys=%llx offset=%llx\n",
 		       __func__, phys, pgmap_phys, data_offset);
-- 
2.53.0