[RFC PATCH v3 1/2] iommu: Add capability IOMMU_CAP_VIOMMU

[Lu Baolu <baolu.lu@linux.intel.com>]

Some vendor IOMMU drivers are able to declare that it is running in a VM
context. This is very valuable for the features that only want to be
supported on bare metal. Add a capability bit so that it could be used.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
---
 drivers/iommu/intel/iommu.c  | 20 ++++++++++++++++++++
 drivers/iommu/virtio-iommu.c |  9 +++++++++
 include/linux/iommu.h        |  1 +
 3 files changed, 30 insertions(+)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index cb205a04fe4c..8eb022d0e8aa 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -5738,12 +5738,32 @@ static inline bool nested_mode_support(void)
 	return ret;
 }
 
+static inline bool caching_mode_enabled(void)
+{
+	struct dmar_drhd_unit *drhd;
+	struct intel_iommu *iommu;
+	bool ret = false;
+
+	rcu_read_lock();
+	for_each_active_iommu(iommu, drhd) {
+		if (cap_caching_mode(iommu->cap)) {
+			ret = true;
+			break;
+		}
+	}
+	rcu_read_unlock();
+
+	return ret;
+}
+
 static bool intel_iommu_capable(enum iommu_cap cap)
 {
 	if (cap == IOMMU_CAP_CACHE_COHERENCY)
 		return domain_update_iommu_snooping(NULL) == 1;
 	if (cap == IOMMU_CAP_INTR_REMAP)
 		return irq_remapping_enabled == 1;
+	if (cap == IOMMU_CAP_VIOMMU)
+		return caching_mode_enabled();
 
 	return false;
 }
diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
index 2bfdd5734844..719793e103db 100644
--- a/drivers/iommu/virtio-iommu.c
+++ b/drivers/iommu/virtio-iommu.c
@@ -931,7 +931,16 @@ static int viommu_of_xlate(struct device *dev, struct of_phandle_args *args)
 	return iommu_fwspec_add_ids(dev, args->args, 1);
 }
 
+static bool viommu_capable(enum iommu_cap cap)
+{
+	if (cap == IOMMU_CAP_VIOMMU)
+		return true;
+
+	return false;
+}
+
 static struct iommu_ops viommu_ops = {
+	.capable		= viommu_capable,
 	.domain_alloc		= viommu_domain_alloc,
 	.domain_free		= viommu_domain_free,
 	.attach_dev		= viommu_attach_dev,
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index b95a6f8db6ff..1d24be667a03 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -94,6 +94,7 @@ enum iommu_cap {
 					   transactions */
 	IOMMU_CAP_INTR_REMAP,		/* IOMMU supports interrupt isolation */
 	IOMMU_CAP_NOEXEC,		/* IOMMU_NOEXEC flag */
+	IOMMU_CAP_VIOMMU,		/* IOMMU can declar running in a VM */
 };
 
 /*
-- 
2.25.1