[PATCH v2 2/5] iommu/amd: Fix DTE clearing and rename iommu_ignore_device()

[Pranjal Shrivastava <praan@google.com>]

The iommu_ignore_device() function currently uses memset() to manually
clear the primary Device Table Entry (DTE), which risks torn writes as
the hardware reads DTEs as atomic 256-bit qwords. Furthermore, clearing
the primary devid in the lookup table before calling setup_aliases()
causes rlookup_amd_iommu() to fail for aliases. This prevents clearing
the DTEs for DMA aliases.

Fix this by replacing the manual memset with a dedicated helper that
invalidates the DTE by clearing the lower 128 bits (having the Valid bit)
first, followed by the upper 128 bits. The cleared state is then
explicitly cloned to all aliases before the lookup tables are nullified.

Rename the function to iommu_disable_device_dma() more accurately
reflects its intent, as we still support IRQ remapping for these devices)

Fixes: 99fc4ac3d297 ("iommu/amd: Introduce per PCI segment alias_table")
Reported-by: sashiko-bot@kernel.org
Closes: https://lore.kernel.org/all/20260529153216.2AD1E1F00899@smtp.kernel.org/
Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Pranjal Shrivastava <praan@google.com>
---
 drivers/iommu/amd/iommu.c | 53 ++++++++++++++++++++++++++-------------
 1 file changed, 36 insertions(+), 17 deletions(-)

diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
index 9b8ad131ba79..911a95527d74 100644
--- a/drivers/iommu/amd/iommu.c
+++ b/drivers/iommu/amd/iommu.c
@@ -728,22 +728,6 @@ static struct iommu_dev_data *iommu_init_device(struct amd_iommu *iommu,
 	return dev_data;
 }
 
-static void iommu_ignore_device(struct amd_iommu *iommu, struct device *dev)
-{
-	struct amd_iommu_pci_seg *pci_seg = iommu->pci_seg;
-	struct dev_table_entry *dev_table = get_dev_table(iommu);
-	int devid, sbdf;
-
-	sbdf = get_device_sbdf_id(dev);
-	if (sbdf < 0)
-		return;
-
-	devid = PCI_SBDF_TO_DEVID(sbdf);
-	pci_seg->rlookup_table[devid] = NULL;
-	memset(&dev_table[devid], 0, sizeof(struct dev_table_entry));
-
-	setup_aliases(iommu, dev);
-}
 
 
 /****************************************************************************
@@ -2233,6 +2217,41 @@ static void dev_update_dte(struct iommu_dev_data *dev_data, bool set)
 		clear_dte_entry(iommu, dev_data);
 }
 
+/*
+ * Invalidate a DTE by clearing the Valid bit first.
+ * Note: Not to be used on a fully probed device with
+ * live dev_data.
+ */
+static void amd_iommu_disable_dte(struct dev_table_entry *ptr)
+{
+	struct dev_table_entry new = {};
+
+	write_dte_lower128(ptr, &new);
+	write_dte_upper128(ptr, &new);
+}
+
+static void iommu_disable_device_dma(struct amd_iommu *iommu, struct device *dev)
+{
+	struct amd_iommu_pci_seg *pci_seg = iommu->pci_seg;
+	struct dev_table_entry *dev_table = get_dev_table(iommu);
+	int devid, sbdf;
+
+	sbdf = get_device_sbdf_id(dev);
+	if (sbdf < 0)
+		return;
+
+	devid = PCI_SBDF_TO_DEVID(sbdf);
+
+	/* Clear the primary DTE */
+	amd_iommu_disable_dte(&dev_table[devid]);
+
+	/* Clone the cleared DTE to all aliases before wiping the rlookup */
+	if (dev_iommu_priv_get(dev))
+		clone_aliases(iommu, dev);
+
+	pci_seg->rlookup_table[devid] = NULL;
+}
+
 /*
  * If domain is SVA capable then initialize GCR3 table. Also if domain is
  * in v2 page table mode then update GCR3[0].
@@ -2521,7 +2540,7 @@ static struct iommu_device *amd_iommu_probe_device(struct device *dev)
 		ret = PTR_ERR(dev_data);
 		dev_err(dev, "Failed to initialize - trying to proceed anyway\n");
 		iommu_dev = ERR_PTR(ret);
-		iommu_ignore_device(iommu, dev);
+		iommu_disable_device_dma(iommu, dev);
 		goto out_err;
 	}
 
-- 
2.55.0.691.gc56d675ccc-goog