[PATCH 2/6] iommu/amd: Clear DTE with update_dte256 in iommu_ignore_device()

[Pranjal Shrivastava]

The iommu_ignore_device() function currently uses memset() to clear
the Device Table Entry (DTE), which risks torn writes because the
hardware reads DTEs as atomic 256-bit qwords. Fix this by using
update_dte256() to perform a hardware-safe atomic clear when a live
dev_data entry is available.

Fixes: 99fc4ac3d297 ("iommu/amd: Introduce per PCI segment alias_table")
Reported-by: sashiko-bot@xxxxxxxxxx
Closes: https://lore.kernel.org/all/20260529153216.2AD1E1F00899@xxxxxxxxxxxxxxx/
Signed-off-by: Pranjal Shrivastava <praan@xxxxxxxxxx>
---
 drivers/iommu/amd/iommu.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index a94de66a885e..9b5861e241d7 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -750,7 +750,16 @@ static void iommu_ignore_device(struct amd_iommu *iommu, struct device *dev)
 	setup_aliases(iommu, dev);
 
 	pci_seg->rlookup_table[devid] = NULL;
-	memset(&dev_table[devid], 0, sizeof(struct dev_table_entry));
+
+	/* Clear DTE if we have a live entry */
+	if (dev_data) {
+		struct dev_table_entry new = {};
+
+		amd_iommu_make_clear_dte(dev_data, &new);
+		update_dte256(iommu, dev_data, &new);
+	} else {
+		memset(&dev_table[devid], 0, sizeof(struct dev_table_entry));
+	}
 }
 
 
-- 
2.54.0.823.g6e5bcc1fc9-goog