[dpdk-dev] [PATCH] igb_uio: map dummy dma forcing iommu domain attachment

[Alejandro Lucero <alejandro.lucero@netronome.com>]

For using a DPDK app when iommu is enabled, it requires to
add iommu=pt to the kernel command line. But using igb_uio driver
makes DMAR errors because the device has not an IOMMU domain.

Since kernel 3.15, iommu=pt requires to use the internal kernel
DMA API for attaching the device to the IOMMU 1:1 mapping, aka
si_domain. Previous versions did attach the device to that
domain when intel iommu notifier was called.

This is not a problem if the driver does later some call to the
DMA API because the mapping can be done then. But DPDK apps do
not use that DMA API at all.

Doing this dma map and unmap is harmless even when iommu is not
enabled at all.

Signed-off-by: Alejandro Lucero <alejandro.lucero@netronome.com>
---
 lib/librte_eal/linuxapp/igb_uio/igb_uio.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/lib/librte_eal/linuxapp/igb_uio/igb_uio.c b/lib/librte_eal/linuxapp/igb_uio/igb_uio.c
index df41e45..f79fe6b 100644
--- a/lib/librte_eal/linuxapp/igb_uio/igb_uio.c
+++ b/lib/librte_eal/linuxapp/igb_uio/igb_uio.c
@@ -326,6 +326,8 @@ struct rte_uio_pci_dev {
 {
 	struct rte_uio_pci_dev *udev;
 	struct msix_entry msix_entry;
+	dma_addr_t map_dma_addr;
+	void *map_addr;
 	int err;
 
 	udev = kzalloc(sizeof(struct rte_uio_pci_dev), GFP_KERNEL);
@@ -423,6 +425,25 @@ struct rte_uio_pci_dev {
 	dev_info(&dev->dev, "uio device registered with irq %lx\n",
 		 udev->info.irq);
 
+	/*
+	 * Doing a harmless dma mapping for attaching the device to
+	 * the iommu identity mapping if kernel boots with iommu=pt.
+	 * Note this is not a problem if no IOMMU at all.
+	 */
+	map_addr = dma_zalloc_coherent(&dev->dev, 1024,
+				       &map_dma_addr, GFP_KERNEL);
+
+	if (!map_addr)
+		dev_info(&dev->dev, "dma mapping failed\n");
+	else {
+		dev_info(&dev->dev, "mapping 1K dma=%#llx host=%p\n",
+			 (unsigned long long)map_dma_addr, map_addr);
+
+		dma_free_coherent(&dev->dev, 1024, map_addr, map_dma_addr);
+		dev_info(&dev->dev, "unmapping 1K dma=%#llx host=%p\n",
+			 (unsigned long long)map_dma_addr, map_addr);
+	}
+
 	return 0;
 
 fail_remove_group:
-- 
1.9.1