[PATCH v2] PCI/P2PDMA: Root complex whitelist should not apply when an IOMMU is present

[Logan Gunthorpe]

Presently, there is no path to DMA map P2PDMA memory, so if a TLP
targeting this memory hits the root complex and an IOMMU is present,
the IOMMU will reject the transaction, even if the RC would support
P2PDMA.

So until the kernel knows to map these DMA addresses in the IOMMU,
we should not enable the whitelist when an IOMMU is present.

Link: https://lore.kernel.org/linux-pci/20190522201252.2997-1-logang@xxxxxxxxxxxx/
Fixes: 0f97da831026 ("PCI/P2PDMA: Allow P2P DMA between any devices under AMD ZEN Root Complex")
Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
Reviewed-by: Christian KÃnig <christian.koenig@xxxxxxx>
Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
---
 drivers/pci/p2pdma.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
index a98126ad9c3a..a4994aa3acc0 100644
--- a/drivers/pci/p2pdma.c
+++ b/drivers/pci/p2pdma.c
@@ -18,6 +18,7 @@
 #include <linux/percpu-refcount.h>
 #include <linux/random.h>
 #include <linux/seq_buf.h>
+#include <linux/iommu.h>
 
 struct pci_p2pdma {
 	struct gen_pool *pool;
@@ -299,6 +300,9 @@ static bool root_complex_whitelist(struct pci_dev *dev)
 	struct pci_dev *root = pci_get_slot(host->bus, PCI_DEVFN(0, 0));
 	unsigned short vendor, device;
 
+	if (iommu_present(dev->dev.bus))
+		return false;
+
 	if (!root)
 		return false;
 
-- 
2.20.1