[PATCH 1/2] iommu/arm-smmu: Fix stream-match conflict with IOMMU_DOMAIN_DMA

[Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org>]

Commit cbf8277ef456 ("iommu/arm-smmu: Treat IOMMU_DOMAIN_DMA as bypass
for now") ignores requests to attach a device to the default domain
since, without IOMMU-basked DMA ops available everywhere, the default
domain will just lead to unexpected transaction faults being reported.

Unfortunately, the way this was implemented on SMMUv2 causes a
regression with VFIO PCI device passthrough under KVM on AMD Seattle.
On this system, the host controller device is associated with both a
pci_dev *and* a platform_device, and can therefore end up with duplicate
SMR entries, resulting in a stream-match conflict at runtime.

This patch amends the original fix so that attaching to IOMMU_DOMAIN_DMA
is rejected even before configuring the SMRs. This restores the old
behaviour for now, but we'll need to look at handing host controllers
specially when we come to supporting the default domain fully.

Reported-by: Eric Auger <eric.auger-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
Tested-by: Eric Auger <eric.auger-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
Tested-by: Yang Shi <yang.shi-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
Signed-off-by: Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org>
---
 drivers/iommu/arm-smmu.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
index 2409e3bd3df2..5158febd889d 100644
--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -1089,18 +1089,20 @@ static int arm_smmu_domain_add_master(struct arm_smmu_domain *smmu_domain,
 	struct arm_smmu_device *smmu = smmu_domain->smmu;
 	void __iomem *gr0_base = ARM_SMMU_GR0(smmu);
 
-	/* Devices in an IOMMU group may already be configured */
-	ret = arm_smmu_master_configure_smrs(smmu, cfg);
-	if (ret)
-		return ret == -EEXIST ? 0 : ret;
-
 	/*
 	 * FIXME: This won't be needed once we have IOMMU-backed DMA ops
-	 * for all devices behind the SMMU.
+	 * for all devices behind the SMMU. Note that we need to take
+	 * care configuring SMRs for devices both a platform_device and
+	 * and a PCI device (i.e. a PCI host controller)
 	 */
 	if (smmu_domain->domain.type == IOMMU_DOMAIN_DMA)
 		return 0;
 
+	/* Devices in an IOMMU group may already be configured */
+	ret = arm_smmu_master_configure_smrs(smmu, cfg);
+	if (ret)
+		return ret == -EEXIST ? 0 : ret;
+
 	for (i = 0; i < cfg->num_streamids; ++i) {
 		u32 idx, s2cr;
 
-- 
2.1.4